1 Samuel 1:4-5, 11

Whenever the day came for Elkanah to sacrifice, he would give portions of the meat to his wife Peninnah and to all her sons and daughters. But to Hannah he gave a double portion because he loved her, and the LORD had closed her womb.

And 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.”