Albert Barnes Commentary 1 Samuel 1:11

"And she vowed a vow, and said, O Jehovah of hosts, if thou wilt indeed look on the affliction of thy handmaid, and remember me, and not forget thy handmaid, but wilt give unto thy handmaid a man-child, then I will give him unto Jehovah all the days of his life, and there shall no razor come upon his head." — 1 Samuel 1:11 (ASV)

Vows are characteristic of this particular age of the Judges (Judges 21:5; 1 Samuel 14:24). For the law of vows in the case of married women, see Numbers 30:6-16; and for the nature of the vow, see the marginal references.