I never saw anybody suffering so much from sickness as Messenger of Allah ﷺ.  

مَا رَأَيْتُ أَحَدًا أَشَدَّ عَلَيْهِ الْوَجَعُ مِنْ رَسُولِ اللَّهِ ﷺ  

I visited the Prophet ﷺ during his ailments and he was suffering from a high fever. I said, "You have a high fever. Is it because you will have a double reward for it?" He said, "Yes, for no Muslim is afflicted with any harm but that Allah will remove his sins as the leaves of a tree fall down."  

عَنْ عَبْدِ اللَّهِ ؓ أَتَيْتُ النَّبِيَّ ﷺ فِي مَرَضِهِ وَهْوَ يُوعَكُ وَعْكًا شَدِيدًا وَقُلْتُ إِنَّكَ لَتُوعَكُ وَعْكًا شَدِيدًا قُلْتُ إِنَّ ذَاكَ بِأَنَّ لَكَ أَجْرَيْنِ قَالَ أَجَلْ مَا مِنْ مُسْلِمٍ يُصِيبُهُ أَذًى إِلاَّ حَاتَّ اللَّهُ عَنْهُ خَطَايَاهُ كَمَا تَحَاتُّ وَرَقُ الشَّجَرِ