Abd Rabbih bin Sa'id bin Qays narrates from his paternal aunt that the Prophet (peace and blessings be upon him) said: "Fever removes the impurities of a human being just as the furnace removes the impurity (that is, the rust) of iron."
Al-Tabarani recorded it in al-Mu'jam al-Kabir. Its chain contains a narrator, Muhammad bin Abi Humayd, and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 3830