Musnad Ahmad 26:312

Zayd ibn Hubab narrated to us, Husayn narrated to me, ‘Asim ibn Bahdalah narrated to me, he said: I heard Shaqiq ibn Salamah saying: I heard Ibn Mas‘ud saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I saw Gabriel at the Lote Tree of the Utmost Boundary, and he had six hundred wings." He said: I asked ‘Asim about the wings, but he refused to tell me. He said: Then some of his companions informed me: "That each wing is [the distance] between the east and the west."