Narrated Ibn `Abbas:Allah's Messenger (ﷺ) 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 (ﷺ) said, "Then it is so."
حَدَّثَنَا مُحَمَّدٌ، حَدَّثَنَا عَبْدُ الْوَهَّابِ الثَّقَفِيُّ، حَدَّثَنَا خَالِدٌ الْحَذَّاءُ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم دَخَلَ عَلَى أَعْرَابِيٍّ يَعُودُهُ فَقَالَ " لاَ بَأْسَ عَلَيْكَ طَهُورٌ، إِنْ شَاءَ اللَّهُ ". قَالَ قَالَ الأَعْرَابِيُّ طَهُورٌ، بَلْ هِيَ حُمَّى تَفُورُ عَلَى شَيْخٍ كَبِيرٍ، تُزِيرُهُ الْقُبُورَ. قَالَ النَّبِيُّ صلى الله عليه وسلم " فَنَعَمْ إِذًا ".
Bukhari
Oneness, Uniqueness of Allah (Tawheed) • Hadith 96