Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyidah Aisha (may Allah be pleased with her) that the Noble Prophet (peace and blessings of Allah be upon him) said: "When a believer falls ill, Allah, the Exalted, purifies him (of sins) just as a furnace removes impurities from iron."

Narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) went to Umm Sa’ib or Umm Musayyib and said: “What is the matter with you? Why are you trembling?” She said: “It is fever; may Allah not bless it.” He (peace and blessings of Allah be upon him) said: “Do not curse fever, for it removes the sins of the children of Adam just as a bellows removes the impurities of iron.”

Sayyiduna Abu Sa'id and Abu Hurairah (may Allah be pleased with them) heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Whatever illness, fatigue, hardship, and sorrow reaches a Muslim, even if he is worried, because of it his sins are forgiven."