Musnad Ahmad 26:655

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Sulayman, who said: I heard Ibrahim al-Taymi, from al-Harith ibn Suwayd, from Abdullah, who said: I entered upon the Messenger of Allah, may Allah bless him and grant him peace, while he was suffering from a fever. I said: "O Messenger of Allah, you are suffering from a severe fever?" The Messenger of Allah, may Allah bless him and grant him peace, said: "Indeed, I suffer from a fever like two men among you." I said: "Is it because you have two rewards?" He said: "Yes—or [it is] a term." Then he said: "There is no Muslim who is afflicted with harm, a thorn or anything beyond it, except that Allah, the Almighty and Majestic, removes his sins from him, just as a tree sheds its leaves."