Musnad Ahmad 652:52

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, from Simak ibn Harb, he said: I heard al-Nu'man ibn Bashir delivering a sermon, saying: I heard the Messenger of Allah (peace and blessings of Allah be upon him) delivering a sermon, saying: "I have warned you of the Fire, I have warned you of the Fire," until even if a man were in the marketplace, he would have heard him from this place of mine. He said: Until a *khamisah* (a garment with markings) that was upon his shoulder fell to his feet.