1 Samuel 1:10-12

10And she was in bitterness of soul, and prayed to the Lord and wept in anguish.

11Then she made a vow and said, “O Lord of hosts, if You will indeed look on the affliction of Your maidservant and remember me, and not forget Your maidservant, but will give Your maidservant a male child, then I will give him to the Lord all the days of his life, and no razor shall come upon his head.”

12And it happened, as she continued praying before the Lord, that Eli watched her mouth.