Shmuel Alef 1:11

And she vowed a neder (vow), and said, O Hashem Tzva'os, if thou wilt indeed look on the misery of thine handmaid, and remember me, and not forget thine handmaid, but wilt give unto thine handmaid zera anashim, then I will give him unto Hashem kol yamei of his chayyah, and there shall no razor come upon his head.