Musnad Abu Ya'la al-Mawsili 115:252

Zuhayr narrated to us, Affan narrated to us, Hammad narrated to us, from Qatadah, Thabit, and Humayd, from Anas: That the Messenger of Allah (ﷺ), Abu Bakr, Umar, and Uthman used to begin the prayer with "Al-hamdu lillahi rabbil-alamin" (Praise be to Allah, Lord of the worlds). And Humayd would not mention the Prophet (ﷺ).