I visited the Messenger of Allah ﷺ while he was suffering from a fever, and I said, "Messenger of Allah, you are burning with a severe fever."The Messenger of Allah ﷺ replied, "I suffer the fever of two men among you."I said, "Is that because you have a double reward?"He answered, "Yes," or he said, "Indeed."Then he continued, "There is no Muslim afflicted by harm, whether the prick of a thorn or anything greater, except that Allah erases his sins through it, just as a tree sheds its leaves."
حدثنا محمد بن جعفر حدثنا شعبة عن سليمان قال سمعت إبراهيم التيمي عن الحارث بن سويد
دخلت على رسول الله ﷺ وهو يوعك فقلت يا رسول الله إنك توعك وعكا شديدا فقال رسول الله ﷺ إني أوعك وعك رجلين منكم قلت بأن لك أجرين قال نعم أو أجل ثم قال ما من مسلم يصيبه أذى شوكة فما فوقها إلا حط الله عز وجل عنه خطاياه كما تحت الشجرة ورقها
Its isnad is sahih, and it is a repetition of 3618, 3619. Al-wak: fever, or it is said its pain, and one says "the illness afflicted him with wak," and he is afflicted, so he is fevered. So said Ibn Athir.