Deuteronomy 23:21-23

The Voice

²¹ When you make a vow to the Eternal, your True God, pay it promptly. He will be looking for you to fulfill your promise; and if you don’t, it will be a sin. ²² It isn’t a sin to make a vow in the first place. ²³ But whatever you do say, you must fulfill completely: you made a vow of your own free will to the Eternal your God, and you must keep your word.