1 Samuel 1:21 - Joseph Benson’s Commentary on the Old and New Testaments

Elkanah and all his house went up Hannah only and her child excepted. And his vow By which it appears, though it was not expressed before, that he heard and consented to her vow; and that he added a vow of his own; probably when he saw his wife was with child; or before, when she told him what hope she had that her prayers would be heard; and when he worshipped God, as mentioned 1 Samuel 1:19.