Deuteronomy 23:21-23

“When you make a vow to the LORD your God, you shall not delay to pay it; for the LORD your God will surely require it of you, and it would be sin to you. But if you abstain from vowing, it shall not be sin to you. That which has gone from your lips you shall keep and perform, for you voluntarily vowed to the LORD your God what you have promised with your mouth.