1 Samuel 1:10-11, 17

And she was in bitterness of soul, and prayed unto the LORD, and wept sore. And she vowed a vow, and said, O LORD of hosts, if thou wilt indeed look on the affliction of thine handmaid, and remember me, and not forget thine handmaid, but wilt give unto thine handmaid a man child, then I will give him unto the LORD all the days of his life, and there shall no razor come upon his head.

Then Eli answered and said, Go in peace: and the God of Israel grant thee thy petition that thou hast asked of him.