Narrated Abu Sa'id Al-Khudri and Abu Huraira: The Prophet said, "No fatigue, nor disease, nor sorrow, nor sadness, nor hurt, nor distress befalls a Muslim, even if it were the prick he receives from a thorn, but that Allah expiates some of his sins for that."
— Sahih Bukhari, Volume 7, Book 70: Patients, Hadith #545