Sahih al-Bukhari, Volume 7, Book 70, Hadith 551 (USC-MSA) ⓘ

Narrated `Abdullah: I visited Allah's Messenger while he was suffering from a high fever. I said, "O Allah's Messenger! You have a high fever." He said, "Yes, I have as much fever as two men of you." I said, "Is it because you will have a double reward?" He said, "Yes, it is so. No Muslim is afflicted with any harm, even if it were the prick of a thorn, but that Allah expiates his sins because of that, as a tree sheds its leaves."

حَدَّثَنَا عَبْدَانُ، عَنْ أَبِي حَمْزَةَ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ التَّيْمِيِّ، عَنِ الْحَارِثِ بْنِ سُوَيْدٍ، عَنْ عَبْدِ اللَّهِ، قَالَ دَخَلْتُ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم وَهْوَ يُوعَكُ فَقُلْتُ يَا رَسُولَ اللَّهِ إِنَّكَ تُوعَكُ وَعْكًا شَدِيدًا‏.‏ قَالَ ‏"‏ أَجَلْ إِنِّي أُوعَكُ كَمَا يُوعَكُ رَجُلاَنِ مِنْكُمْ ‏"‏‏.‏ قُلْتُ ذَلِكَ أَنَّ لَكَ أَجْرَيْنِ قَالَ ‏"‏ أَجَلْ ذَلِكَ كَذَلِكَ، مَا مِنْ مُسْلِمٍ يُصِيبُهُ أَذًى شَوْكَةٌ فَمَا فَوْقَهَا، إِلاَّ كَفَّرَ اللَّهُ بِهَا سَيِّئَاتِهِ، كَمَا تَحُطُّ الشَّجَرَةُ وَرَقَهَا ‏"‏‏.‏