Musnad Ahmad 394:1

Abu Amir narrated to us, he said: Abdullah ibn Abi Sulayman, a righteous sheikh of good appearance from Medina, narrated to us, he said: Mu'adh ibn Abdullah ibn Khubayb narrated to us, from his father, from his uncle, who said: "We were in a gathering when the Messenger of Allah, may Allah bless him and grant him peace, appeared before us." [He then mentioned the rest of the hadith].