Musnad Ahmad 26:71

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim al-Taymi, from Al-Harith ibn Suwayd, from Abdullah, who said: I entered upon the Prophet, peace and blessings of Allah be upon him, while he was suffering from a fever. I touched him and said: "O Messenger of Allah, you are suffering from a severe fever?" He said: "Yes, I suffer from a fever as two men among you suffer." I said: "Is it because you have two rewards?" He said: "Yes. By the One in whose hand is my soul, there is no Muslim on earth who is afflicted with harm, from illness or anything else, but that Allah removes his sins from him because of it, just as a tree sheds its leaves."