Deuteronomy 23:21-23 - Keeping Vows
21 When you take an oath to the Lord, do not be slow to give effect to it: for without doubt the Lord your God will make you responsible, and will put it to your account as sin 22 But if you take no oath, there will be no sin. 23 Whatever your lips have said, see that you do it; for you gave your word freely to the Lord your God.