And his vow— It is most likely that Elkanah had united with Hannah in the vow she made, 1 Samuel 1:11 and moreover had promised, in case of its completion, to offer some extraordinary sacrifice.
Related Commentaries of 1 Samuel 1:21
1 Samuel 1:21
21 And the man Elkanah, and all his house, went up to offer unto the LORD the yearly sacrifice, and his vow.