2,849. Beginning Hilchos Nezirus

Hilchos Nedarim 13:25

The Sages said that a person who makes a vow is like one who has built a private altar (which is prohibited). If a person violates the law by making a vow, it is a mitzvah for him to approach a Torah scholar to have it absolved; in this way the vow will no longer serve as an obstacle in his path. This is the case when it comes to vows of prohibition; when it comes to vows of consecration, it is a mitzvah to keep them and not to seek their absolution unless one’s circumstances are dire, as per Psalms 116:14, “I will fulfill my vows to Hashem.”

Hilchos Nezirus 1:1

A nazirite vow is a vow of prohibition, as per Numbers 6:2, “When a person takes a nazirite vow to abstain for Hashem....” It is a Torah obligation for a nazir to let the hair of his head grow, as per verse 5, “He shall let the growth of the hair of his head grow.” If he cuts his hair during the days of his nazirite obligation, he violates a Torah prohibition, as the same verse says, “a razor shall not pass over his head.” He is likewise prohibited to be rendered ritually unclean by a corpse and to eat the products of a grape vine that the Torah specifically prohibits for the entire duration of his nazirite period.