There is a widespread custom to stay up all night on Shavuos engaged in Torah study. The Magen Avraham (494) writes that this custom is rooted in a midrash that says the Jewish people at Mount Sinai overslept on the day of the giving of the Torah, and Hashem had to wake them up to present it to them. To rectify their mistake and to prevent ourselves from making a similar one, we demonstrate our eagerness to once again receive the Torah by remaining awake the entire night.
A man whose pregnant wife was at the end of her ninth month wanted to spend Shavuos night – with his wife’s consent – learning Torah in his yeshiva. He planned to place a cell phone near his designated seat before Yom Tov, which his wife could call if she went into labor and needed him to come home and escort her to the hospital. However, he wondered whether it was halachically sound to lechatchila place himself into a situation that might require his wife to call him (permissibly) when he could instead remain home to learn on his own, which he recognized would likely result in him eventually dozing off.
Rav Yitzchok Zilberstein responded that at first glance, it would appear that he could go out to learn on Shavuos night. Since at the time he leaves there is no indication that his wife will need to call him, he is not causing any desecration of Yom Tov. If her situation subsequently changes, she is allowed to call him using a shinuy [deviation from the normal manner, such as dialing with a utensil].
This is seemingly analogous to the ruling of the Shulchan Aruch (Orach Chaim 248:4) that a person may set out with a caravan on Friday to travel through the desert to Eretz Yisroel, and if he finds himself in danger on Shabbos, he may then perform whatever melacha [creative work] is necessary to save his life. The Mishnah Berurah explains that because the person departed lawfully and the danger only arose later, anything he does at that point to save his life is not deemed a desecration of Shabbos.
Similarly, Rav Shlomah Zalman Auerbach (Shemiras Shabbos K’Hilchaso 40n64) permits a doctor who is on call on Shabbos to remain home with his family. Even though he knows in advance that the hospital may call him regarding patients whose lives are in danger, the mitzvah of Oneg Shabbos [enjoying Shabbos] is sufficient to exempt him from being required to spend the entire Shabbos in the hospital to reduce the risk of having to do melacha on Shabbos.
On the other hand, the Steipler (Kehillas Yaakov, Shabbos 15) maintains that a person is only allowed to place himself in a situation that may eventually require him to do melacha on Shabbos to save a life if he does so before Shabbos has begun. He explains that before the onset of Shabbos, a person is not yet obligated in its laws, so creating circumstances that may compel him to do work once Shabbos has begun is considered grama [an indirection action], which is permissible.
Once Shabbos has already begun and a person is commanded to sanctify it, any action he takes that may subsequently cause melacha to be done – even for pikuach nefesh [saving a life] – is already deemed to be desecrating Shabbos, even before any actual work was done. Because nobody is in danger at that time, there is no justification of pikuach nefesh, and it is therefore forbidden to desecrate Shabbos in this manner, even to do a mitzvah.
Accordingly, it would be forbidden for the husband to go out to learn on Shavuos night, as once Yom Tov has begun, he may not take any actions that could later require him to do melacha to save a life. Indeed, when this question was presented to Rav Chaim Kanievsky, he ruled in accordance with the opinion of his father (the Steipler) and forbade the husband to go to yeshiva on Shavuos night.
(Taken from R’ Ozer Alport’s, Parsha Potpourri)
