Numbers 30:2

2 When a man makes a vow to the Lord or swears an oath to put himself under an obligation, he must not break his word; he must do whatever he has promised.

Numbers 30:2 In-Context

1 Moses told the leaders of the Israelite tribes, "This is what the Lord has commanded:
2 When a man makes a vow to the Lord or swears an oath to put himself under an obligation, he must not break his word; he must do whatever he has promised.
3 "When a woman in her father's house during her youth makes a vow to the Lord or puts [herself] under an obligation,
4 and her father hears about her vow or the obligation she put herself under, and he says nothing to her, all her vows and every obligation she put herself under are binding.
5 But if her father prohibits her on the day he hears [about it], none of her vows and none of the obligations she put herself under are binding. The Lord will absolve her because her father has prohibited her.
Holman Christian Standard Bible ® Copyright © 2003, 2002, 2000, 1999 by Holman Bible Publishers.  Used by permission.  All rights reserved.