Deuteronomy 23:21-23 - Keeping Vows
21 When you vow to Jehovah your God do not delay the payback. It would be sin, and Jehovah your God will surely require it of you. 22 It would not be sin if you refrain from vowing. 23 Be careful to perform the promise that comes from your lips, just as you have voluntarily vowed to Jehovah your God. Keep your promise.