Musnad Ahmad 30:1388

'Affan narrated to us, 'Abd al-Wahid narrated to us, 'Asim ibn Kulayb narrated to us, my father narrated to me, that he heard Abu Hurayrah say: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever sees me in a dream, then he has indeed seen me, for the Shaytan does not impersonate me." 'Asim said: My father said: Then Ibn 'Abbas narrated it to me. So I informed him that I had seen him [the Prophet]. He said: "You saw him?" I said: "Yes, by Allah, I have indeed seen him." He said: Then I mentioned Al-Hasan ibn 'Ali. He said: "I have, by Allah, mentioned him, and I described his gait." He said: Then Ibn 'Abbas said: "He used to resemble him."