Musnad Ahmad 32:1672

'Affan narrated to us, Hammad ibn Salamah narrated to us, Abu Rabi'ah narrated to us, from Anas ibn Malik: That the Messenger of Allah (peace and blessings of Allah be upon him) entered upon a Bedouin to visit him while he was feverish. He said: "An expiation and a purification." The Bedouin said: "Rather, a fever boiling upon an old man, visiting him to the graves." So the Messenger of Allah (peace and blessings of Allah be upon him) stood up and left him.