1 Samuel 1:10-11

10Hannah was greatly distressed, and she prayed to the Lord and wept in anguish.

11She made a vow, saying, “O Lord of hosts, if You will indeed look on the affliction (suffering) of Your maidservant and remember, and not forget Your maidservant, but will give Your maidservant a son, then I will give him to the Lord all the days of his life; a razor shall never touch his head.”