Deuteronomy 23:21-23

New Revised Standard Version, Anglicised Catholic Edition

²¹ If you make a vow to the Lord your God, do not postpone fulfilling it; for the Lord your God will surely require it of you, and you would incur guilt. ²² But if you refrain from vowing, you will not incur guilt. ²³ Whatever your lips utter you must diligently perform, just as you have freely vowed to the Lord your God with your own mouth.