It is narrated from Sayyidah Umm al-Ala' (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) came to her during her illness and said: "Rejoice, O Umm al-Ala'! For the illness of a Muslim removes his sins just as fire removes the dross of iron."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21802