Though only one person (he) is mentioned, the context suggests that a plural is in view and thus it was Hannah, Elkanah, and Samuel who worshipped the Lord. The Hebrew text contains a variant word from which suggests that it was originally a plural and not a singular.1
28 Aussi je veux le prêter à l'Eternel: il sera toute sa vie prêté à l'Eternel. Et ils se prosternèrent là devant l'Eternel.