Sahih Bukhari
Oneness, Uniqueness of Allah (Tawheed)
Volume: 009 / Book Number: 093 / Hadith Number: 562
Narrated Ibn 'Abbas:
Allah's Apostle entered upon a sick bedouin in whom he went to visit and said to him, "Don't worry, Tahur (i.e., your illness will be a means of cleansing of your sins), if Allah Will." The bedouin said, "Tahur! No, but it is a fever that is burning in the body of an old man and it will make him visit his grave." The Prophet said, "Then it is so."