Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) went to a Bedouin to visit him while he was in a state of fever. The Prophet (peace and blessings be upon him) said: "(This illness) will be a means of expiation and purification." The Bedouin said: "No, rather it is a fever that is boiling over an old man, and it will not rest until it has brought him to the grave." So the Prophet (peace and blessings be upon him) got up and left him (to his state).
Ahmad recorded it, and its narrators are thiqat (trustworthy). I say: Later the hadith narrated from Sayyiduna Shurahbil (may Allah be pleased with him) will come in the chapter on the one who is patient through fever and hopes for reward; in it
this narration will come more clearly.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 3781