Musnad Ahmad 1153:1320

'Abd al-Razzaq narrated to us, he said: Ma'mar informed us, from al-Zuhri, from 'Urwah, from 'Aishah, she said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There is no illness or pain that afflicts a believer but that it is an expiation for his sin, even the thorn that pricks him or the stumble he stumbles."