Musnad Ahmad 435:96

Muhammad ibn Abdullah ibn al-Zubayr narrated to us, Umar ibn Sa’id narrated to us, he said: Ali ibn Abdullah ibn Ali informed me, my father informed me, that he heard Mu’awiyah delivering a sermon in the shade of the Kaaba, and he was saying: "The Messenger of Allah, peace and blessings of Allah be upon him, forbade gold jewelry and the wearing of silk."