Musnad Ahmad 30:562

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, from Nafi', the freed slave of Abu Qatadah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "How will you be when the son of Mary descends among you, and your leader—or he said: your Imam—is from among you?"