1 Samuel 1:9-12

9Once when they had finished eating and drinking in Shiloh, Hannah stood up. Now Eli the priest was sitting on his chair by the doorpost of the LORD ’s house. 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.” 12As she kept on praying to the LORD, Eli observed her mouth.