Musnad Ahmad 1153:147

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim, from Al-Aswad, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "A believer is not afflicted by a thorn or anything beyond it, except that Allah, the Almighty and Majestic, raises him a degree by it and removes a sin from him by it."