1 Samuel 1:10-11

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.”