Musnad Ahmad 31:23

Isma'il ibn Ibrahim narrated to us, Muhammad ibn Ishaq informed us, from Muhammad ibn 'Amr ibn 'Ata', from 'Ata' ibn Yasar, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The believer is not afflicted with fatigue, nor weariness, nor sadness, nor illness, nor harm—even the anxiety that worries him—but that Allah expiates some of his sins thereby."