Abu Burdah bin Abi Musa al-Ash'ari (may Allah have mercy on him) said: I went in to Mu'awiyah (may Allah be pleased with him) while he was tossing and turning in pain, and he had a sore between his shoulders. He said: I would not be pleased not to have what you see. I heard the Messenger of Allah (peace and blessings be upon him) say: "No harm afflicts a believer in his body except that it becomes an expiation for his sins."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16890