Musnad Abu Ya'la al-Mawsili 245:21

Abu Ubaydah ibn Fudayl ibn Iyad narrated to us, Abu Sa'id narrated to us, Abd al-Rahman Abu al-Ala narrated to us, Muhammad ibn Muhajir narrated to us, from Kaysan, the freed slave of Mu'awiyah, who said: Mu'awiyah delivered a sermon to us and said: "Indeed, the Messenger of Allah (peace and blessings of Allah be upon him) forbade seven things, and I forbid you from them. Know that among them are wailing, singing, images, poetry, gold, the skins of predatory animals, displaying one's adornments (tabarruj), and silk."