Musnad Ahmad 25:527

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Husayn ibn Abdullah ibn Ubaydullah ibn Abbas narrated to us, from Ikrimah, the freed slave of Abdullah ibn Abbas, from Abdullah ibn Abbas, who said: "I indeed saw the Messenger of Allah, may Allah bless him and grant him peace, on a rainy day, and he was protecting himself from the mud when he prostrated with a garment he had on him, placing it between his hands and the ground when he prostrated."