Musnad Ahmad 31:346

Abu Abd al-Rahman narrated to us, Ismail narrated to us, Sulayman ibn Abi Zaynab narrated to me, from Yazid ibn Muhammad al-Qurashi, from Abu Sa’id al-Khudri, from the Messenger of Allah (peace and blessings of Allah be upon him) that he said: "No worry, nor sadness, nor fatigue, nor illness, nor harm befalls a believer, except that Allah expiates [sins] by it for him."