1 Samuel 1:10-11

10In her deep anguish Hannah prayed to the LORD, weeping bitterly.

11And she made a vow, saying, “ LORD Almighty, if you will only look on your servant’s misery and remember me, and not forget your servant but give her a son, then I will give him to the LORD for all the days of his life, and no razor will ever be used on his head.”