Deuteronomy 23:21-23

New International Version

²¹ If you make a vow to the Lord your God, do not be slow to pay it,^(A) for the Lord your God will certainly demand it of you and you will be guilty of sin.^{(B) 22} But if you refrain from making a vow, you will not be guilty.^{(C) 23} Whatever your lips utter you must be sure to do, because you made your vow freely to the Lord your God with your own mouth.