Musnad Ahmad 1153:1385

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Sulayman, from Ibrahim, from al-Aswad, from 'Aishah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There is no Muslim who is pricked by a thorn, or anything greater than it, except that Allah raises him a degree by it, and removes a sin from him by it."