Reference for I Chronicles 15:26

וַֽיְהִי֙ בֶּעְזֹ֣ר הָֽאֱלֹהִ֔ים אֶ֨ת־הַלְוִיִּ֔ם נֹשְׂאֵ֖י אֲר֣וֹן בְּרִית־יְהוָ֑ה וַיִּזְבְּח֥וּ שִׁבְעָֽה־פָרִ֖ים וְשִׁבְעָ֥ה אֵילִֽים׃

And it came to pass, when God helped the Levites that bore the ark of the covenant of the LORD, that they sacrificed seven bullocks and seven rams.