Musnad Abu Ya'la al-Mawsili 147:51

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Hammad narrated to us, from Sinan Abu Rabi'ah, 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. The Prophet (peace and blessings of Allah be upon him) said: "An expiation and a purification." The Bedouin said: "Rather, a fever boiling upon an old man, visiting him to the graves." So the Prophet (peace and blessings of Allah be upon him) stood up and left him.