Musnad Ahmad 30:2096

Ali ibn Ishaq narrated to us, Abdullah informed us, Ubaydullah ibn Abd al-Rahman ibn Abdullah ibn Mawhab informed us, he said: My paternal uncle Ubaydullah ibn Abdullah ibn Mawhab narrated to me, he said: I heard Abu Hurairah saying: The Messenger of Allah, may Allah bless him and grant him peace, said: "There is no believer who is pricked by a thorn in this world, and he seeks reward for it, except that some of his sins are cut away by it on the Day of Resurrection."