2 Samuel 15:8

And she vowed a vow, and said, O LORD of hosts, if thou wilt indeed look on the affliction of thine handmaid, and remember me, and not forget thine handmaid, but wilt give unto thine handmaid a man child, then I will give him unto the LORD all the days of his life, and there shall no razor come upon his head.

So Joab arose and went to Geshur, and brought Absalom to Jerusalem.

Because ye have said, We have made a covenant with death, and with hell are we at agreement; when the overflowing scourge shall pass through, it shall not come unto us: for we have made lies our refuge, and under falsehood have we hid ourselves:

And Absalom answered Joab, Behold, I sent unto thee, saying, Come hither, that I may send thee to the king, to say, Wherefore am I come from Geshur? it had been good for me to have been there still: now therefore let me see the king’s face; and if there be any iniquity in me, let him kill me.

And Samuel said, How can I go? if Saul hear it, he will kill me. And the LORD said, Take an heifer with thee, and say, I am come to sacrifice to the LORD.

For ye dissembled in your hearts, when ye sent me unto the LORD your God, saying, Pray for us unto the LORD our God; and according unto all that the LORD our God shall say, so declare unto us, and we will do it.

Thy vows are upon me, O God: I will render praises unto thee.

And if it seem evil unto you to serve the LORD, choose you this day whom ye will serve; whether the gods which your fathers served that were on the other side of the flood, or the gods of the Amorites, in whose land ye dwell: but as for me and my house, we will serve the LORD.

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.