1 Samuel 1:9-11

9Once after a sacrificial meal at Shiloh, Hannah got up and went to pray. Eli the priest was sitting at his customary place beside the entrance of the Tabernacle.

10Hannah was in deep anguish, crying bitterly as she prayed to the Lord.

11And she made this vow: “O Lord of Heaven’s Armies, if you will look upon my sorrow and answer my prayer and give me a son, then I will give him back to you. He will be yours for his entire lifetime, and as a sign that he has been dedicated to the Lord, his hair will never be cut.”