There was a case when someone came to daven in a place where there were a number of minyonim taking place, and on his way in he saw a chosson who was in his week of Sheva Berachos. This individual then went to daven for the amud, and when he finished shemonah esrei he immediately said kaddish, and omitted tachanun, as he thought there was a chosson in his minyan. After reciting kaddish he realized that there was no chosson in sight and that the chosson must have attended a different minyan. What is the halachah in this case, may tachanun still be recited even though the chazon said kaddish? If yes, should kaddish be repeated a second time?
L'Horas Nossan
The Shu”t L’Horas Nossan (6:7) discusses a similar question and he writes that although the Beis Yosef (beginning of 131) writes that one shouldn’t speak between the end of shemonah esrei and tachanun as it is one long tefillah, however, the poskim say that bedieved if one did speak, he may still recite tachanun, it’s just that it won’t be as potent.
The Taz in Hilchos Aveilus (Yoreh Deah 376:2) brings in the name of the Roke’ach that we don’t recite tachanun in a beis avel [house of mourning], however, after davening one should make sure to recite tachanun. We see clearly from the Roke’ach, that even if there has been a kaddish interrupting between shemonah esrei and tachanun, it may still be recited.
Practically we don’t rule like this (see Taz in Hilchos Tefillah, Orach Chaim 131 s.k. 9), however, the L’Horas Nossan says that this is specifically by a beis avel when one is exempt from saying tachanun (see Shulchan Aruch 131:4) and since one isn’t supposed to say it after shemoneh esrei, it should no longer be said, as in such a case Chazal never required it. Like the Shulchan Aruch HaRav (131:5) writes: “The place for tachanun is immediately after shemonah esrei, and in a beis avel where we push aside tachanun from being recited in its normal place, we push it aside completely”. However, in our case of the non-existent chosson, where the chazon mistakenly recited kaddish and omitted tachanun, everyone would agree that tachanun should be recited, and mistakenly missing it out doesn’t uproot the chiyuv. Especially, after we have seen from the Roke’ach, that even by a beis avel tachanun should be recited later on. When tachanun is omitted with a good reason then there is no need to recite it later, but when it is omitted due to a mistake, then one must make it up.
Based on this, the L’Horas Nossan concludes that tachanun should be recited later, even if one has finished davening, and he adds that kaddish should be recited a second time after tachanun.
R’ Shlomah Zalman Auerbach (Halichos Shlomah Vol. 1, 11:2) also rules that tachanun should be recited. He adds: If krias haTorah has already been recited and the chazon realizes before Ashrei and U’Vo LeTzion, tachanun should be recited then and the tzibbur shouldn’t wait. Although there is room to argue that since this isn’t the ideal place for tachanun, and the chazon is considered to be in the middle of his tefillah until after Ashrei and U’Vo LeTzion (see Mishnah Berurah 123:18), perhaps he should wait, nonetheless it is still best to recite it there.
However, they bring a story with the Chazon Ish (Orchos Rabbeinu, Vol. 3, pg. 225) that one time he was in a minyan and the chazon omitted tachanun and started kaddish, and the Chazon Ish ruled that he should continue, and tachanun should no longer be recited. R’ Chaim Kanievsky zt”l explained this pesak, that since tachanun is a continuation of shemonah esrei like we mentioned from the Beis Yosef, if one interrupts, one has lost the continuation and it should no longer be said.
Conclusion
There is a machlokes haposkim what to do if the chazon accidently skips out tachanun, some say it should still be recited, and some say once it has been skipped there is no going back. Practically I heard from R’ Boruch Dzialowski shlita, that when it comes to shailos in tachanun, we say sofek tachanun lekulah [when doubts arise about whether to say tachanun or not, we rule leniently and omit it] (this is based on a Sha’ar HaTziyun, and a ruling of R’ Chaim Kanievsky zt”l) and therefore, in this case we would not go back.
