It is narrated from Sayyiduna Abd al-Rahman bin Azhar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The example of the believing servant when he is struck by fever or its heat is just like a piece of iron that is put into the fire: its dross is removed and its pure, good part remains." The chain of this hadith is sahih (authentic); its narrators are Madinans and Egyptians, and the two Shaykhs did not record it.