Musnad Abu Ya'la al-Mawsili 109:84

Ubayd Allah ibn Umar al-Qawariri narrated to us, Yazid ibn Zuray' narrated to us, al-Hajjaj ibn al-Sawwaf narrated to us, from Abu al-Zubayr, who said: Jabir ibn Abdullah narrated to me that the Messenger of Allah (may Allah bless him and grant him peace) entered upon Umm al-Sa'ib or Umm al-Musayyab while she was shivering. He said: "What is the matter with you, O Umm al-Sa'ib or O Umm al-Musayyab, that you are shivering?" She said: "The fever, may Allah not bless it." He said: "Do not curse the fever, for it removes the sins of the son of Adam just as the bellows removes the dross of iron."