Musnad Ahmad 32:597

'Abd al-Samad narrated to us, Hammad narrated to us, from Thabit, from Anas, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When Allah created Adam, He left him for as long as Allah willed to leave him. So Iblis began to circle around him, looking at him. When he saw that he was hollow, he knew that he was a creation that would not be able to control himself."