Deuteronomy 23:21-23

Thomson(i) 21 If thou vowest a vow to the Lord thy God, thou shalt not delay to pay it; for the Lord thy God will surely require it of thee; and it would be a sin in thee. 22 If thou dost not chuse to make a vow, it is no sin in thee. 23 Thou must be careful of what have proceeded from thy lips; and offer, in the manner thou hast vowed to the Lord thy God, the gift which thou hast promised with thy mouth.