Deuteronomy 23:21-23

Living Bible

²¹ “When you make a vow to the Lord, be prompt in doing whatever it is you promised him, for the Lord demands that you promptly fulfill your vows; it is a sin if you don’t. ²² (But it is not a sin if you refrain from vowing!) ²³ Once you make the vow, you must be careful to do as you have said, for it was your own choice, and you have vowed to the Lord your God.