Deuteronomy 23:21-23

Young's Literal Translation

²¹ `When thou vowest a vow to Jehovah thy God, thou dost not delay to complete it; for Jehovah thy God doth certainly require it from thee, and it hath been in thee -- sin.

²² `And when thou forbearest to vow, it is not in thee a sin.

²³ The produce of thy lips thou dost keep, and hast done [it], as thou hast vowed to Jehovah thy God; a free-will-offering, which thou hast spoken with thy mouth.