Deuteronomy 23:21-23 - Keeping Vows
21 When thou shalt vow a vow unto Yahweh thy God, thou shalt not delay to make it good, - for Yahweh thy God would, require, it of thee, and it should be in thee sin. 22 But, if thou refrain from vowing, it shall not be in thee sin. 23 That which goeth forth out of thy lips, thou must observe and do, - according as thou didst vow unto Yahweh thy God the free-will, offering of which thou didst speak with thy mouth.