Narrated 'Abdullah: I visited the Prophet salallahu'alaihi wassalam during his illness and touched him while he was having a fever. I said to him, "You have a high fever; is it because you will get a double reward?" He said, "Yes. No Muslim is afflicted with any harm, but that his sins will be annulled as the leave of a tree fall down." [Hadith from Sahih Bukhari, Volume 7, Book 70: Patients, Number 565].