Musnad Ahmad 4346

Translation

✧ I entered upon the Prophet ﷺ while he was suffering from a fever. I placed my hand on him and said, 'You are suffering from a severe fever!' He said, 'Indeed, I suffer a fever like two men of you.' I said, 'That is because you have a double reward?' He said, 'Yes. There is no believer who is afflicted by illness or anything else except that Allah thereby sheds his sins, just as a tree sheds its leaves.'

Grades by grader