Siman 341

We learned in the Mishna at the end of Shabbat (157a): "One may annul vows on Shabbat, and one may request absolution for vows that are for the need of Shabbat." That is to say, by the letter of the law it should have been forbidden to release vows on Shabbat, for this is not among the matters of Heaven, and it is forbidden for the reason of "pursuing your own affairs." However, regarding the annulment of a husband for his wife or a father for his daughter, where if he does not annul on the day he hears the vow remains established and he will no longer be able to annul, they permitted annulling any vow on Shabbat. But for the absolution of a sage, one may only request absolution when the vow pertains to the need of Shabbat, such as if he vowed that he would not eat meat or that he would not drink wine, and certainly if he vowed that he would not eat at all or not drink at all. And even if he vowed that he would not wear a significant garment, it is called a need of Shabbat. The same law applies to a vow that pertains to another matter of mitzvah when they release it for him—it is permitted to release it on Shabbat (Turei Zahav), and there is one who forbids (Maharsha at the beginning of "Bekhol Me'arvin," see there). And the first opinion appears primary, for since it pertains to a matter of mitzvah, it is like the matters of Heaven. And in the Mishna where we learned "for the need of Shabbat," it taught the common case, and certainly for a complete matter of mitzvah, and one may request absolution even if they were able to request absolution before Shabbat (the Rambam chapter 24).

In Yoreh Deah siman 234 it was explained that when one annuls on Shabbat, he should not say to her: "It is annulled for you" in the manner that he says on a weekday, but rather he says to her: "Take and eat, take and drink" and thinks the annulment in his heart; see there. However, for the hatarat chacham, he must of necessity say: "It is permitted to you," for if not so, it is not a hatarah. And one of the great authorities wrote: "Regarding excommunication in a dream, we have performed an action and permitted it on Shabbat (Knesset HaGedolah and Eliyahu Rabbah)." And know that sometimes it is found that one may inquire of a chacham even not for the need of Shabbat, such as a husband who ratified the vows of his wife and we maintain that he may inquire of a chacham regarding his ratification, as is written there, and there are those who hold that this is specifically on the day of hearing; see there. If so, it follows that if he does not inquire today, he will not be able to annul, and if so, its law is like the annulment itself (Tuv Ta'am VeDa'at).

And it is a simple matter that if the husband does not yet know of his wife's nedarim, they should not tell him on Shabbat, and when he hears tomorrow he shall annul them for her on the day of his hearing, unless the neder pertains to the needs of Shabbat. And so too if she is a betrothed maiden and her father has already heard her neder, then it is necessary to inform the betrothed man as well so that they both may annul in partnership, according to what we maintain there that both of them must hear on the same day (ibid.). And know that according to what has been explained in Yoreh Deah siman 323 regarding challah that fell into a cooked dish and there is not enough to nullify it, that they may seek an inquiry regarding the challah and remove it from its sanctity—certainly it is permitted to seek an inquiry on Shabbat and permit it, for this is a need of Shabbat (Sh"t).

One who swore to perform a certain labor and that the labor would be completed on a certain day, and it did not happen for him to perform it until the final day of that time and that day occurs on Shabbat, and at the time of his statement he did not think that this would be on Shabbat, such as if he calculated by the days of the month or by the number of days—he must necessarily ask on Shabbat regarding his vow, and they release him on Shabbat by means of an opening or regret. (In the Shulchan Aruch it is written: "And he has openings to release his vow," see there, and it is not specifically so, for we maintain in Yoreh Deah siman 228 that we open with regret. And that which is written in the Shulchan Aruch that with communal bans they practiced to release on Shabbat even if it is not for the need of Shabbat, it has already been explained in siman 306 that all communal needs we consider as matters of Heaven, see there).