Sahih al-Bukhari, Book 75, Hadith 23 (In-Book) ⓘ

Narrated Ibn `Abbas: Allah's Messenger entered upon sick man to pay him a visit, and said to him, "Don't worry, Allah willing, (your sickness will be) an expiation for your sins." The man said, "No, it is but a fever that is boiling within an old man and will send him to his grave." On that, the Prophet said, "Then yes, it is so."

حَدَّثَنَا إِسْحَاقُ، حَدَّثَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنْ خَالِدٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم دَخَلَ عَلَى رَجُلٍ يَعُودُهُ فَقَالَ ‏"‏ لاَ بَأْسَ طَهُورٌ إِنْ شَاءَ اللَّهُ ‏"‏‏.‏ فَقَالَ كَلاَّ بَلْ حُمَّى تَفُورُ عَلَى شَيْخٍ كَبِيرٍ كَيْمَا تُزِيرَهُ الْقُبُورَ‏.‏ قَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ فَنَعَمْ إِذًا ‏"‏‏.‏