Musnad Ahmad 30:157

Sufyan narrated to us, from al-Zuhri, from Abd al-Rahman al-A’raj, who said: I heard Abu Hurayrah saying: You claim that Abu Hurayrah narrates many hadiths from the Messenger of Allah (peace and blessings of Allah be upon him), and Allah is the Promised One. I was a poor man, accompanying the Messenger of Allah (peace and blessings of Allah be upon him) for the sake of filling my stomach. The Emigrants (Muhajirun) were occupied by trading in the marketplaces, and the Helpers (Ansar) were occupied by tending to their wealth. I was present at a gathering with the Prophet (peace and blessings of Allah be upon him), and he said: "Whoever spreads out his garment until I finish my speech, then gathers it to himself, will never forget anything he heard from me." So I spread out the cloak I was wearing until he finished his speech, then I gathered it to myself. By the One in Whose hand is my soul, I have not forgotten anything after I heard it from him.