Numbers 6:2

6:2 “Speak to the Israelites, and tell them, ‘When either a man or a woman takes a special vow, to take a vow as a Nazirite, to separate himself to the Lord,

Numbers 30:2

30:2 If a man makes a vow to the Lord or takes an oath of binding obligation on himself, he must not break his word, but must do whatever he has promised.