I Samuel 1:4-5, 11

And whenever the time came for Elkanah to make an offering, he would give portions to Peninnah his wife and to all her sons and daughters. But to Hannah he would give a double portion, for he loved Hannah, although the LORD had closed her womb.

Then 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.”