Sahih Bukhari
Patients
Volume: 007 / Book Number: 070 / Hadith Number: 550
Narrated 'Abdullah:
I visited the Prophet 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."