Deuteronomy 23:22-24

22But if thou shalt forbear to vow, it shall be no sin in thee. 23That which is uttered by thy lips thou shalt keep and perform; even a freewill offering, according as thou hast vowed to the LORD thy God, which thou hast promised with thy mouth. 24When thou comest into thy neighbour’s vineyard, then thou mayest satisfy thy appetite with grapes at thy own pleasure; but thou shalt not put any in thy vessel.