Musnad Ahmad 32:1670

'Affan narrated to us, Bishr ibn al-Mufaddal narrated to us, Humayd narrated to us, from Anas, who said: "I never heard him narrate a hadith from the Prophet, may Allah bless him and grant him peace, except that he would say: 'Or as the Messenger of Allah, may Allah bless him and grant him peace, said.'"