וַיְהִ֣י הַיּ֔וֹם וַיִּזְבַּ֖ח אֶלְקָנָ֑ה וְנָתַ֞ן לִפְנִנָּ֣ה אִשְׁתּ֗וֹ וּֽלְכָל־בָּנֶ֛יהָ וּבְנוֹתֶ֖יהָ מָנֽוֹת׃
И было, что в тот день, когда Елкана принес жертву, он дал Пенинне, жене своей, и всем сыновьям ее и дочерям ее порции;
Radak
And it was on that day: The day of the set time; and likewise did Yonatan translate it [in the Targum] as, "the day of the set time." And in the homiletical teachings: Rabbi Yehoshua be Levi said, "This was the day of Shavuot."
Metzudat David
And it was on that day: Meaning to say, when the day came that he would bring his sacrifices, Elkanah would sacrifice peace-offerings and he would give portions to Peninah, etc. from the sacrifice of the peace-offerings.