Divergent Minhogim in One Shul
Limuday Moshe | July 04, 2024
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Divergent Minhogim in One Shul

Limuday Moshe | June 27, 2025

In this week’s parsha we learn about one of the most difficult, ongoing, and ageless problems in the world – strife, or in Hebrew: machlokes. Korach and his assembly approached Moshe Rabbenu to challenge his status as leader, and that of his brother Aharon as Kohen Gadol. As a result, Korach, Dasan, Aviram and their families were miraculously swallowed in the earth, and their assembly of two hundred and fifty men were burned alive. This left a large bald spot in Klal Yisroel.

The Yalkut Shimoni (Re’eh 891) commenting on the words לא תתגודדו in Parshas Re’eh writes:לא תתגודדו לא תשימו אגודות אגודות ותהיו חלוקין אלו על אלו שלא תשימו קרחה בכם כשם שעשה קרח שחלק לישראל ועשאן אגודות אגודות ועשה קרחה בישראל שנבלעו עמי בני אדם הרבה- “Don’t form separate groups amongst yourselves which argue with each other. (Making sure not to do so) will ensure that there is no bald spot created in Klal Yisroel. Don’t follow in the ways of Korach, who divided Klal Yisroel into separate groups and caused a great bald spot to be created - as he caused many people to get swallowed up with him”.

The Yalkut Shimoni is warning us not to get into fights and make different groups in Klal Yisroel, doing so will end up creating bald spots in Klal Yisroel. Korach formed a group of people which opposed the leadership of Moshe Rabbeinu, they caused lots of strife, and the end result was that 250 people were wiped out, causing a bald spot to be created in Klal Yisroel. The Medrash is alluding to the fact that the words Korach and korcha [bald spot] are related, and we need to learn from Korach not to get into fights as the end results are far from something desirable, and it may lead to bald spots being created in Klal Yisroel.

The simple meaning of the words לא תתגודדו has nothing to do with machlokes. The simple peshat [understanding] in the pasuk is, that there is a prohibition for one to wound himself when mourning for someone who has passed away. There used to be a practice common amongst idol worshippers, that when someone would die, in order to show grief over what had happened, they would wound themselves. The pasuk is coming to warn against such a practice and is saying: “You shall neither cut yourselves (לא תתגודדו) nor make any baldness between your eyes for the dead” (Devorim 14:1).”

However, the Gemara in Yevamos (13b) understands that had the Torah intended only to forbid cutting flesh in sign of mourning there would have been no reason for the plural form of the word. From the fact that the Torah writes לא תתגודדו in plural form, we darshen [expound]: לא תעשו אגודות אגודות – “Don’t form divergent groups”, that the Jewish nation is commanded to remain unified, and there is a negative commandment against breaking up into subgroups.

Why Is There No Prohibition of תתגודדו לא By Reading Megillah?

The Mishnah in Megillah (2a) teaches: “Megillah can be read on the 11th, 12th, 13th, 14th and 15th, no earlier and no later”. There are five alternative dates for when Megillas Esther can be read. If one lives in a non-walled city then he reads on the 14th, if one lives in a walled city from the days of Yehoshua bin Nun then he reads on the 15th, etc.

The question is, why is this not a problem of תתגודדו לא? The truth is, the Gemara in Yevamos (13b) asks this very question. Before answering the question, the Gemara discusses how we learn from לא תתגודדו that there is a prohibition of לא תעשו אגודות אגודות – “Don’t form subgroups”, and the Gemara concludes like we mentioned, that we learn it from the fact that לא תתגודדו is written in the plural.

Eventually the Gemara (14a) answers: “There is only a problem if there is a disagreement between two Botei Dinim in the same town. If it is amongst two Botei Dinim in two different towns then it’s ok”. Although Megillah is read in different places at different times, in any specific place it is read at one time, therefore, there is no concern.

In the question of the Gemara, Rashi explains that the problem of לא תתגודדו is: דנראה כנוהגין ב׳ תורות – “It looks like there are two Torah’s”. We will return to this Rashi shortly.

We see from the above Gemara, that in one town there shouldn’t be opposing minhogim [customs] taking place. The reason for this is it causes strife, and as the Yalkut warns, it could ultimately lead to creating bald patches in Klal Yisroel.

De’O’raisa or Derabonon [Torah Law or Rabbinic]?

The Rambam (Sefer HaMitzvos, Lo Saseh 45) writes: “We are warned against making wounds in our body, like what is commonly done by those people who serve avodah zorah, Hashem warns, “Don’t cut yourself”.

The Rambam continues: “It is said, included in this prohibition is a warning against having two Botei Dinim in the same city each articulating a different way of how to act when it comes to a certain halachah. This is learnt from the pasuk לא תתגודדו, however, the literal meaning of the pasuk is like we said, ‘not to make wounds’”.

The Rambam concludes: וזה הוא כמו דרש – “This second prohibition we learn from the pasuk is a darash [reliance, but not a proper drosha]”.

The Rambam continues: We find a similar concept by the prohibition of maintaining an already existing fight (being machzik bemachlokes) which we learn from the pasuk: “Do not be like Korach and his assembly”. We make a drosha from the pasuk, however, the pasuk isn’t really coming to teach this.

From the aforementioned Rambam it seems very clear that the prohibition of לא תעשו אגודות אגודות – “Don’t form divergent groups”, is nothing more than an issur derabonon.

However, from the Rambam in Yad HaChazakah it would seem that the Rambam holds otherwise. In Yad HaChazakah the Rambam (Hilchos Avodah Zorah 12:13-14) writes: “Just like the non-Jews wound themselves when mourning due to grief, they do the same thing when serving avodah zorah. This practice is also prohibited due to the prohibition of לא תתגודדו ...” The Rambam continues: “Included in this prohibition is that there shouldn’t be two Botei Dinim in the same city, one following this custom, and another following this custom. Such a things causes big disputes, and it writes לא תתגודדו, from which we learn, לא תעשו אגודות אגודות – “Don’t form divergent groups””.

From the aforementioned Rambam in Yad HaChazakah we see very clearly that th Rambam maintains that the prohibition of “forming divergent groups” is an issur de’O’raisa.

The Sdei Chemed (Mareches Lo Sisgoidadu) notes this contradiction, and he says that the Rambam simply changed his mind. When he wrote Sefer HaMitzvos he held that the prohibition was Rabbinic in nature, however, by the time he got around to writing Yad HaChazakah he changed his mind, and held that it’s prohibited on a Torah level.

We will see below, that most poskim take on like the Rambam in Yad Chazakah that the prohibition is an issur de’O’raisa and is prohibited on a Torah level.

What Is Behind the Prohibition?

If we analyze the Rambam carefully, we will see that he has a different understanding to Rashi, as to what is behind the prohibition of לא תתגודדו.

Earlier we mentioned Rashi in Yevamos. Rashi learns that the issue is: דנראה כנוהגין ב׳ תורות – “It looks like there are two Torah’s”. If different groups of people and different Botei Dinim act differently it gives off the impression that there are two different Torah’s, and perhaps chas vesholam more than one Ribbono Shel Olam.

The Rambam, however, explains that the problem is: גדולה למחלוקת גורם זה שדבר – “Such a matter causes big disputes”. The Rambam understands, the issue is not that it looks like two Torah’s, rather, if there are two opposing customs it causes strife and machlokes.

The Yalkut Shimoni we started with seems to understand like the Rambam, that the problem of לא תתגודדו is that it causes fights and creates bald spots in Klal Yisroel. Anyone who has been to daven in a shul will know this to be true – different minhogim causes fights.

Practical Difference

Is there any practical difference that comes out from the machlokes between Rashi and the Rambam?

Yes, we will see below a very big practical difference:

The Netziv (Meishiv Dovar 1:17) was asked the following shailah:

“If an Ashkenazi is in a place where they are davening nussach Sephard, what should he do regarding the nussach which he davens in? Additionally, what should he do when it comes to answering kedusha, is he allowed to answer in accordance with minhag Sephard, or should he answer in accordance with minhag Ashkenaz?”

Does לא תתגודדו Apply to Minhogim Aswell?

The Netziv writes, that seemingly it would depend on whether the din of לא תתגודדו only applies to concrete dinim [laws], or if it applies to minhogim [customs] as well. From the Gemara in Yevamos which deals with when Megillah should be read, it would seem that the din of לא תתגודדו only applies to concrete dinim and not things which are simply minhogim. The din of Megillah being read on various different dates is learnt from a pasuk (בזמניהם), therefore, לא תתגודדו applies. When it comes to minhogim however, perhaps לא תתגודדו doesn’t apply.

When it comes to an Ashkenazi davening nussach Sephard or vice versa, it may not be ideal, however, no one says that one doesn’t fulfill his obligation to daven by doing so, therefore, perhaps the din of לא תתגודדו doesn’t apply.

What Does This Depend On?

The Netziv explains that the above would seemingly depend on the machlokes between Rashi and the Rambam. If we learn like the Rambam that the issue is שדבר זה גורם למחלוקת גדולה – “Such a matter causes big disputes”, then it wouldn’t make a difference if it is a din or a minhag, either way people will start fighting. If, however, we learn like Rashi that the issue is דנראה כנוהגין ב׳ תורות – “It looks like there are two Torah’s”, then it would only apply to dinim which are learnt from the Torah. If it is something which is just a minhag, then there is no concern of “looking like two Torah’s” as the minhag is not coming from the Torah.

In short, the question of whether לא תתגודדו applies to minhogim is a machlokes between Rashi and the Rambam, according to the Rambam it does, and according to Rashi it doesn’t.

How Do We Rule?

The Mechaber (Orach Chaim 493:3) writes: “Some have the custom to have haircuts starting from Rosh Chodesh Iyar, this is a mistake”. The Rema then writes: “However, in many places the custom is to have haircuts until Rosh Chodesh Iyar. In such places they shouldn’t have haircuts from Lag B’Omer and on, however, on Lag B’Omer itself they may. In those places that have the custom to have haircuts from Lag B’Omer and on, they shouldn’t have any haircuts from Pesach until Lag B’Omer. In one city there shouldn’t be some people keeping one custom, and another group of people keeping a second custom, as this is an issue of לא תתגודדו ...”.

We see from the Rema, that even on something which is simply a minhag, there is still a problem of לא תתגודדו. Consequently, it would seem that halachah lema’aseh [practically] we follow the Rambam.

Conclusion

The Netziv concludes, since we rule like the Rambam who learns that the problem of לא תתגודדו is שדבר זה גורם למחלוקת גדולה – “such a matter causes big disputes”. If an Ashkenazi finds himself in a Sephardi minyan, when it comes to parts of tefillah which are said quietly, he should daven nussach Ashkenaz - since no one can hear, there is no reason for a fight to break out. However, when it comes to answering kedusha which is done loudly and everyone can hear then the Ashkenazi should daven nussach Sephard.

In short: When he can daven nussach Ashkenaz and no one will know he should, and when it comes to parts of davening which can’t be kept quiet then he should daven nussach Sephard.

Wearing Tefillin On Chol HaMo’ed

Another common shailah related to לא תתגודדו, is the shailah of whether it is ok for people who wear tefillin on Chol HaMo’ed to daven together in the same minyan as people who hold that doing so is prohibited.

The Sdei Chemed (Mareches, Chol HaMo’ed, ois 14) addresses this shailah. The Sdei Chemed quotes the Malbim (Artzois HaChaim) who rules, that it is forbidden to have in the same minyan, some people wearing tefillin and some not. If people aren’t careful about this, then it is a prohibition of לא תתגודדו.

The Sdei Chemed quotes a sefer which writes: “The Mishnah Berurah of my dear friend Meir HaKohen Av Beis Din of Radin writes, it’s not correct that in one shul there are some people who wear tefillin and some who don’t, doing so is a violation of לא תתגודדו”.

The Sdei Chemed quotes a Teshuvah from R’ Chaim Aryeh Horowitz who suggests that there is no problem of לא תתגודדו. He suggests: Since the people who wear tefillin don’t make a berachah when wearing tefillin, they are in effect saying that they themselves are unsure about what is correct. Since even those who wear tefillin are unsure, perhaps there is no issue of לא תתגודדו. There is only machlokes if one groups holds strongly one way, and one group holds strongly the other way, if however, the group that wears tefillin is also in doubt, perhaps it makes things easier.

However, the Sdei Chemed and other poskim reject the above argument.

Many shuls are very makpid [particular] about the above and avoid having mixed minyonim. Either they have one minyan for those who wear tefillin, and another one for those who don’t. Or they tell those who want to wear tefillin to daven in the ezras noshim.

R' Moshe Feinstein (Igros Moshe, Orach Chaim 4:34) was asked the above shailah, and he paskened that לא תתגודדו is an issur de’O’raisa, and that the shul must have two separate minyonim.

In the aforementioned Teshuvah, R’ Moshe writes: If one has the minhag to say viduy and Yud Gimmel Middos before tachanun and he is davening in a shul where the minhag is not to, if one doesn’t follow the shuls minhag he transgresses on לא תתגודדו. He writes, however, that if such a person recites viduy quietly, without clapping, then it’s ok (this is like the Netziv, that there is only a problem if it’s done publicly).

In this week’s parsha we learn about one of the most difficult, ongoing, and ageless problems in the world – strife, or in Hebrew: machlokes. Korach and his assembly approached Moshe Rabbenu to challenge his status as leader, and that of his brother Aharon as Kohen Gadol. As a result, Korach, Dasan, Aviram and their families were miraculously swallowed in the earth, and their assembly of two hundred and fifty men were burned alive. This left a large bald spot in Klal Yisroel.

The Yalkut Shimoni (Re’eh 891) commenting on the words לא תתגודדו in Parshas Re’eh writes:לא תתגודדו לא תשימו אגודות אגודות ותהיו חלוקין אלו על אלו שלא תשימו קרחה בכם כשם שעשה קרח שחלק לישראל ועשאן אגודות אגודות ועשה קרחה בישראל שנבלעו עמי בני אדם הרבה- “Don’t form separate groups amongst yourselves which argue with each other. (Making sure not to do so) will ensure that there is no bald spot created in Klal Yisroel. Don’t follow in the ways of Korach, who divided Klal Yisroel into separate groups and caused a great bald spot to be created - as he caused many people to get swallowed up with him”.

The Yalkut Shimoni is warning us not to get into fights and make different groups in Klal Yisroel, doing so will end up creating bald spots in Klal Yisroel. Korach formed a group of people which opposed the leadership of Moshe Rabbeinu, they caused lots of strife, and the end result was that 250 people were wiped out, causing a bald spot to be created in Klal Yisroel. The Medrash is alluding to the fact that the words Korach and korcha [bald spot] are related, and we need to learn from Korach not to get into fights as the end results are far from something desirable, and it may lead to bald spots being created in Klal Yisroel.

The simple meaning of the words לא תתגודדו has nothing to do with machlokes. The simple peshat [understanding] in the pasuk is, that there is a prohibition for one to wound himself when mourning for someone who has passed away. There used to be a practice common amongst idol worshippers, that when someone would die, in order to show grief over what had happened, they would wound themselves. The pasuk is coming to warn against such a practice and is saying: “You shall neither cut yourselves (לא תתגודדו) nor make any baldness between your eyes for the dead” (Devorim 14:1).”

However, the Gemara in Yevamos (13b) understands that had the Torah intended only to forbid cutting flesh in sign of mourning there would have been no reason for the plural form of the word. From the fact that the Torah writes לא תתגודדו in plural form, we darshen [expound]: לא תעשו אגודות אגודות – “Don’t form divergent groups”, that the Jewish nation is commanded to remain unified, and there is a negative commandment against breaking up into subgroups.

Why Is There No Prohibition of תתגודדו לא By Reading Megillah?

The Mishnah in Megillah (2a) teaches: “Megillah can be read on the 11th, 12th, 13th, 14th and 15th, no earlier and no later”. There are five alternative dates for when Megillas Esther can be read. If one lives in a non-walled city then he reads on the 14th, if one lives in a walled city from the days of Yehoshua bin Nun then he reads on the 15th, etc.

The question is, why is this not a problem of תתגודדו לא? The truth is, the Gemara in Yevamos (13b) asks this very question. Before answering the question, the Gemara discusses how we learn from לא תתגודדו that there is a prohibition of לא תעשו אגודות אגודות – “Don’t form subgroups”, and the Gemara concludes like we mentioned, that we learn it from the fact that לא תתגודדו is written in the plural.

Eventually the Gemara (14a) answers: “There is only a problem if there is a disagreement between two Botei Dinim in the same town. If it is amongst two Botei Dinim in two different towns then it’s ok”. Although Megillah is read in different places at different times, in any specific place it is read at one time, therefore, there is no concern.

In the question of the Gemara, Rashi explains that the problem of לא תתגודדו is: דנראה כנוהגין ב׳ תורות – “It looks like there are two Torah’s”. We will return to this Rashi shortly.

We see from the above Gemara, that in one town there shouldn’t be opposing minhogim [customs] taking place. The reason for this is it causes strife, and as the Yalkut warns, it could ultimately lead to creating bald patches in Klal Yisroel.

De’O’raisa or Derabonon [Torah Law or Rabbinic]?

The Rambam (Sefer HaMitzvos, Lo Saseh 45) writes: “We are warned against making wounds in our body, like what is commonly done by those people who serve avodah zorah, Hashem warns, “Don’t cut yourself”.

The Rambam continues: “It is said, included in this prohibition is a warning against having two Botei Dinim in the same city each articulating a different way of how to act when it comes to a certain halachah. This is learnt from the pasuk לא תתגודדו, however, the literal meaning of the pasuk is like we said, ‘not to make wounds’”.

The Rambam concludes: וזה הוא כמו דרש – “This second prohibition we learn from the pasuk is a darash [reliance, but not a proper drosha]”.

The Rambam continues: We find a similar concept by the prohibition of maintaining an already existing fight (being machzik bemachlokes) which we learn from the pasuk: “Do not be like Korach and his assembly”. We make a drosha from the pasuk, however, the pasuk isn’t really coming to teach this.

From the aforementioned Rambam it seems very clear that the prohibition of לא תעשו אגודות אגודות – “Don’t form divergent groups”, is nothing more than an issur derabonon.

However, from the Rambam in Yad HaChazakah it would seem that the Rambam holds otherwise. In Yad HaChazakah the Rambam (Hilchos Avodah Zorah 12:13-14) writes: “Just like the non-Jews wound themselves when mourning due to grief, they do the same thing when serving avodah zorah. This practice is also prohibited due to the prohibition of לא תתגודדו ...” The Rambam continues: “Included in this prohibition is that there shouldn’t be two Botei Dinim in the same city, one following this custom, and another following this custom. Such a things causes big disputes, and it writes לא תתגודדו, from which we learn, לא תעשו אגודות אגודות – “Don’t form divergent groups””.

From the aforementioned Rambam in Yad HaChazakah we see very clearly that th Rambam maintains that the prohibition of “forming divergent groups” is an issur de’O’raisa.

The Sdei Chemed (Mareches Lo Sisgoidadu) notes this contradiction, and he says that the Rambam simply changed his mind. When he wrote Sefer HaMitzvos he held that the prohibition was Rabbinic in nature, however, by the time he got around to writing Yad HaChazakah he changed his mind, and held that it’s prohibited on a Torah level.

We will see below, that most poskim take on like the Rambam in Yad Chazakah that the prohibition is an issur de’O’raisa and is prohibited on a Torah level.

What Is Behind the Prohibition?

If we analyze the Rambam carefully, we will see that he has a different understanding to Rashi, as to what is behind the prohibition of לא תתגודדו.

Earlier we mentioned Rashi in Yevamos. Rashi learns that the issue is: דנראה כנוהגין ב׳ תורות – “It looks like there are two Torah’s”. If different groups of people and different Botei Dinim act differently it gives off the impression that there are two different Torah’s, and perhaps chas vesholam more than one Ribbono Shel Olam.

The Rambam, however, explains that the problem is: גדולה למחלוקת גורם זה שדבר – “Such a matter causes big disputes”. The Rambam understands, the issue is not that it looks like two Torah’s, rather, if there are two opposing customs it causes strife and machlokes.

The Yalkut Shimoni we started with seems to understand like the Rambam, that the problem of לא תתגודדו is that it causes fights and creates bald spots in Klal Yisroel. Anyone who has been to daven in a shul will know this to be true – different minhogim causes fights.

Practical Difference

Is there any practical difference that comes out from the machlokes between Rashi and the Rambam?

Yes, we will see below a very big practical difference:

The Netziv (Meishiv Dovar 1:17) was asked the following shailah:

“If an Ashkenazi is in a place where they are davening nussach Sephard, what should he do regarding the nussach which he davens in? Additionally, what should he do when it comes to answering kedusha, is he allowed to answer in accordance with minhag Sephard, or should he answer in accordance with minhag Ashkenaz?”

Does לא תתגודדו Apply to Minhogim Aswell?

The Netziv writes, that seemingly it would depend on whether the din of לא תתגודדו only applies to concrete dinim [laws], or if it applies to minhogim [customs] as well. From the Gemara in Yevamos which deals with when Megillah should be read, it would seem that the din of לא תתגודדו only applies to concrete dinim and not things which are simply minhogim. The din of Megillah being read on various different dates is learnt from a pasuk (בזמניהם), therefore, לא תתגודדו applies. When it comes to minhogim however, perhaps לא תתגודדו doesn’t apply.

When it comes to an Ashkenazi davening nussach Sephard or vice versa, it may not be ideal, however, no one says that one doesn’t fulfill his obligation to daven by doing so, therefore, perhaps the din of לא תתגודדו doesn’t apply.

What Does This Depend On?

The Netziv explains that the above would seemingly depend on the machlokes between Rashi and the Rambam. If we learn like the Rambam that the issue is שדבר זה גורם למחלוקת גדולה – “Such a matter causes big disputes”, then it wouldn’t make a difference if it is a din or a minhag, either way people will start fighting. If, however, we learn like Rashi that the issue is דנראה כנוהגין ב׳ תורות – “It looks like there are two Torah’s”, then it would only apply to dinim which are learnt from the Torah. If it is something which is just a minhag, then there is no concern of “looking like two Torah’s” as the minhag is not coming from the Torah.

In short, the question of whether לא תתגודדו applies to minhogim is a machlokes between Rashi and the Rambam, according to the Rambam it does, and according to Rashi it doesn’t.

How Do We Rule?

The Mechaber (Orach Chaim 493:3) writes: “Some have the custom to have haircuts starting from Rosh Chodesh Iyar, this is a mistake”. The Rema then writes: “However, in many places the custom is to have haircuts until Rosh Chodesh Iyar. In such places they shouldn’t have haircuts from Lag B’Omer and on, however, on Lag B’Omer itself they may. In those places that have the custom to have haircuts from Lag B’Omer and on, they shouldn’t have any haircuts from Pesach until Lag B’Omer. In one city there shouldn’t be some people keeping one custom, and another group of people keeping a second custom, as this is an issue of לא תתגודדו ...”.

We see from the Rema, that even on something which is simply a minhag, there is still a problem of לא תתגודדו. Consequently, it would seem that halachah lema’aseh [practically] we follow the Rambam.

Conclusion

The Netziv concludes, since we rule like the Rambam who learns that the problem of לא תתגודדו is שדבר זה גורם למחלוקת גדולה – “such a matter causes big disputes”. If an Ashkenazi finds himself in a Sephardi minyan, when it comes to parts of tefillah which are said quietly, he should daven nussach Ashkenaz - since no one can hear, there is no reason for a fight to break out. However, when it comes to answering kedusha which is done loudly and everyone can hear then the Ashkenazi should daven nussach Sephard.

In short: When he can daven nussach Ashkenaz and no one will know he should, and when it comes to parts of davening which can’t be kept quiet then he should daven nussach Sephard.

Wearing Tefillin On Chol HaMo’ed

Another common shailah related to לא תתגודדו, is the shailah of whether it is ok for people who wear tefillin on Chol HaMo’ed to daven together in the same minyan as people who hold that doing so is prohibited.

The Sdei Chemed (Mareches, Chol HaMo’ed, ois 14) addresses this shailah. The Sdei Chemed quotes the Malbim (Artzois HaChaim) who rules, that it is forbidden to have in the same minyan, some people wearing tefillin and some not. If people aren’t careful about this, then it is a prohibition of לא תתגודדו.

The Sdei Chemed quotes a sefer which writes: “The Mishnah Berurah of my dear friend Meir HaKohen Av Beis Din of Radin writes, it’s not correct that in one shul there are some people who wear tefillin and some who don’t, doing so is a violation of לא תתגודדו”.

The Sdei Chemed quotes a Teshuvah from R’ Chaim Aryeh Horowitz who suggests that there is no problem of לא תתגודדו. He suggests: Since the people who wear tefillin don’t make a berachah when wearing tefillin, they are in effect saying that they themselves are unsure about what is correct. Since even those who wear tefillin are unsure, perhaps there is no issue of לא תתגודדו. There is only machlokes if one groups holds strongly one way, and one group holds strongly the other way, if however, the group that wears tefillin is also in doubt, perhaps it makes things easier.

However, the Sdei Chemed and other poskim reject the above argument.

Many shuls are very makpid [particular] about the above and avoid having mixed minyonim. Either they have one minyan for those who wear tefillin, and another one for those who don’t. Or they tell those who want to wear tefillin to daven in the ezras noshim.

R' Moshe Feinstein (Igros Moshe, Orach Chaim 4:34) was asked the above shailah, and he paskened that לא תתגודדו is an issur de’O’raisa, and that the shul must have two separate minyonim.

In the aforementioned Teshuvah, R’ Moshe writes: If one has the minhag to say viduy and Yud Gimmel Middos before tachanun and he is davening in a shul where the minhag is not to, if one doesn’t follow the shuls minhag he transgresses on לא תתגודדו. He writes, however, that if such a person recites viduy quietly, without clapping, then it’s ok (this is like the Netziv, that there is only a problem if it’s done publicly).

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