Daily Mitzvah (Rambam)

We are commanded to practice the Torah-mandated procedure in the event that a vow is to be annulled.

(This commandment is somewhat based on the verse [Numbers 30:3] "he shall not profane his word," from which the Sages deduce that the one who enacted the vow may not profane his own word, but others – such as a sage or rabbinical court – may do so. Nevertheless, the Talmud says that the "annulment of vows flies in the air, with no [explicit biblical] support...")

The Torah explicitly tells us that a husband and father can nullify vows, and tradition teaches that a sage, too, has the power to do so.

The 95th mitzvah is that we are commanded regarding the annulment of vows.

This does not mean that there is a commandment to annul vows, but rather that there are certain laws to be followed when doing so. You should keep this principle in mind whenever a mitzvah is enumerated — it does not necessarily mean that we are commanded to perform a certain action, but rather that a certain case [whenever it comes up,] must be judged according to certain laws.

The annulment of vows done by a father [to his daughter] and a husband [to his wife] is explained in the Torah1 in detail.

Furthermore, we know from the Oral Tradition that a Torah scholar can nullify anyone's vow or oath. This is hinted to in the verse,2 "He must not nullify his word." [The Sages3 explain,] "He may not nullify his word, but others may nullify it for him." The final conclusion is that there is no real source in Scripture [for the Torah scholar's power to annul a vow, and the verse quoted above is only a hint]. As our Sages4 put it, "The laws regarding the annulment of vows [by a Torah scholar] are flying in the air, with nothing to support them" — except in the Oral Tradition.

The details of this mitzvah are found in the tractate devoted to this subject, tractate Nedarim.