Deuteronomy 23:21-23

“When you make a vow to the LORD your God, you shall not delay to pay it, for He will most certainly require it of you, and a delay would cause you to sin. But if you refrain from making a vow, that would not be [counted as] sin in you. You shall be careful to perform that [vow] which passes your lips, just as you have made a voluntary vow to the LORD your God, just as you have promised with your own words (mouth).