Musnad Ahmad 5:623

Abdullah narrated to us, Hajjaj ibn Yusuf al-Sha'ir narrated to me, Abd al-Samad ibn Abd al-Warith narrated to me, Yazid ibn Abi Salih narrated to us, that Abu al-Wadi' 'Abbad narrated to him, that he said: We were heading toward Kufa with Ali ibn Abi Talib. When we reached a distance of two or three nights' travel from Harura', many people broke away from us. We mentioned that to Ali, and he said: "Do not let their affair alarm you, for they will return." He then mentioned the hadith at length. He said: Ali ibn Abi Talib praised Allah and said: "My intimate friend (the Prophet) informed me that the leader of these people is a man with a deformed hand, upon the nipple of whose breast are hairs like the tail of a jerboa. Seek him out." So they sought him but did not find him. We came to him and said: "We did not find him." He said: "Seek him out, for by Allah, I have not lied, nor have I been lied to," repeating it three times. We said: "We did not find him." Then Ali came himself and began saying: "Turn this over, turn this over," until a man from Kufa came. He said: "Here he is." Ali said: "Allah is the Greatest. Does no one come to you who can tell you whose son he is?" The people began saying: "This is Malik, this is Malik." Ali said: "Whose son is he?"