Mishkat al-Masabih 1538
‘Abdallah b. Mas'ud said:
I went in to visit the Prophet when he was jaded by fever, and touching him with my hand, I said, “You are seriously jaded by fever, messenger of God.” The Prophet replied, “Yes, I am twice as jaded as any of you.” I said, “That is because you have a double reward.” He replied that that was so and then said, “No Muslim is afflicted by injury, be it illness or something else, without God thereby causing his sins to drop away just as a tree sheds its leaves.”
 
(Bukhari and Muslim.)
وَعَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ قَالَ: دَخَلْتُ عَلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَهُوَ يُوعَكُ فَمَسِسْتُهُ بِيَدِي فَقُلْتُ: يَا رَسُولَ اللَّهِ إِنَّكَ لَتُوعَكُ وَعْكًا شَدِيدًا. فَقَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أَجَلْ إِنِّي أُوعَكُ كَمَا يُوعَكُ رَجُلَانِ مِنْكُمْ» . قَالَ: فَقُلْتُ: ذَلِكَ لِأَنَّ لَكَ أَجْرَيْنِ؟ فَقَالَ: «أَجَلْ» . ثُمَّ قَالَ: «مَا مِنْ مُسْلِمٍ يُصِيبُهُ أَذًى مِنْ مَرَضٍ فَمَا سِوَاهُ إِلَّا حَطَّ اللَّهُ تَعَالَى بِهِ سَيِّئَاتِهِ كَمَا تَحُطُّ الشَّجَرَةُ وَرَقَهَا»