Mukhtasar Muslim

It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) went to Umm Sa'ib (or Umm Musayyib) (may Allah be pleased with her), and said: "O Umm Sa'ib (or Umm Musayyib)! You are trembling, what has happened to you?" She replied, "It is fever, may Allah not bless it." The Prophet (peace and blessings be upon him) said: "Do not speak ill of fever, for it removes the sins of people just as a furnace removes the impurities of iron."