Deuteronomy 23:22-24

New Catholic Bible

²² If you make a vow to the Lord, your God, do not be lax in paying it off, for the Lord, your God, will certainly require it of you, and you would be guilty of a sin. ²³ But if you fail to make a vow, there is no sin. ²⁴ Whatever your lips utter, you must do, for you have vowed a freewill offering to the Lord, your God, with your own mouth.