Deuteronomy - Chapter 23

We have in this chapter another instruction on taking vows:

“When you make a vow to the Lord your God, be prompt in fulfilling whatever you promised him. For the Lord your God demands that you promptly fulfill all your vows, or you will be guilty of sin. However, it is not a sin to refrain from making a vow. But once you have voluntarily made a vow, be careful to fulfill your promise to the Lord your God.

Jesus speaks on this in the Sermon on the Mount (Matthew 5):

“You have also heard that our ancestors were told, ‘You must not break your vows; you must carry out the vows you make to the Lord.’ But I say, do not make any vows! Do not say, ‘By heaven!’ because heaven is God’s throne. And do not say, ‘By the earth!’ because the earth is his footstool. And do not say, ‘By Jerusalem!’ for Jerusalem is the city of the great King. Do not even say, ‘By my head!’ for you can’t turn one hair white or black. Just say a simple, ‘Yes, I will,’ or ‘No, I won’t.’ Anything beyond this is from the evil one."