Vows are addressed in Ecclesiastes 5, in Numbers 30, and in the Sermon on the Mount.
4 When thou vowest a vow unto God, defer not to pay it; for he hath no pleasure in fools: pay that which thou hast vowed. 5 Better is it that thou shouldest not vow, than that thou shouldest vow and not pay.
In Numbers 30:2:
2 If a man vow a vow unto the LORD, or swear an oath to bind his soul with a bond; he shall not break his word, he shall do according to all that proceedeth out of his mouth.
In Matthew 5:37:
37 But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.