1 Samuel 1:4-5, 11

On the days Elkanah presented his sacrifice, he would give portions of the meat to Peninnah and each of her children. And though he loved Hannah, he would give her only one choice portion because the LORD had given her no children.

And 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.”