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.
