A father or husband may nullify his daughter’s or his wife’s vows on Shabbat, and one may request from a Sage to dissolve vows that are for the purpose of Shabbat. Failure to dissolve the vow will compromise one’s fulfillment of the mitzva to delight in Shabbat.
The halakhot of vows and their nullification are stated in the Torah (Bamidbar, Chapter 30) and explained in an entire tractate, tractate Nedarim. In essence, when either a young woman still under her father’s auspices or a married woman takes a vow, her father or her husband respectively can nullify the vow on the day that he hears it if he does not approve of it. The Sages explained based on the verses that this is permitted only in certain situations. Only vows taken with regard to matters between the woman and her husband or between the young woman and her father can be nullified. Vows that do not affect the woman’s relationship with her husband or father cannot be nullified. Vows may not only be nullified; one may also request that a sage dissolve his vow. Although this does not appear explicitly in the Torah, the Sages found allusions to it in the same portion.
One who took a vow can request that a single Sage or a court of three dissolve it. Tractate Nedarim deals extensively with the problems that arise in this process. The standard scenario involves the person who took the vow declaring that he did not initially anticipate that it would be so difficult to fulfill the vow, and had he known, he would not have taken the vow in the first place. There is no designated time frame for dissolving one’s vows and one can request that his vows be dissolved at any time. There are also some vows that a Sage cannot dissolve, e.g., a vow made to another person, which would require that person’s agreement to dissolve it. In addition, a vow cannot be dissolved if it was taken before a large group and was contingent on their agreement.