Deuteronomy 23:21-23

Modern English Version

²¹ When you make a vow to the Lord your God, you must not be slow to pay it, for the Lord your God will surely require it of you, and it would be a sin to you. ²² But if you refrain from making a vow, it will not be a sin to you. ²³ That which goes out of your lips you must keep and do, even a freewill offering, just as you have vowed to the Lord your God, what you have promised with your mouth.