Musnad Abu Ya'la al-Mawsili 160:212

Al-Hasan ibn 'Arafah al-'Abdi narrated to us, Abdullah ibn Ibrahim al-Ghaffari narrated to us, from Abd al-Rahman ibn Zayd ibn Aslam, from Sa'id ibn Abi Sa'id, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I was ascended to the lowest heaven, and I did not pass by a heaven except that I found in it my name, 'Muhammad the Messenger of Allah,' and 'Abu Bakr the Truthful' behind me."