Musnad Ahmad 435:50

'Abd al-Samad narrated to us, Harb—meaning Ibn Shaddad—narrated to us, he said: Yahya—meaning Ibn Abi Kathir—narrated to me, he said: Abu Shaykh al-Huna'i narrated to me, from his brother Hamman, that Mu'awiyah, in the year he performed Hajj, gathered a group of the companions of the Messenger of Allah (may Allah bless him and grant him peace) in the Ka'bah. He said: "I am asking you about things, so inform me. I adjure you by Allah, did the Messenger of Allah (may Allah bless him and grant him peace) forbid the wearing of silk?" They said: "Yes." He said: "And I bear witness." Then he said: "I adjure you by Allah, did the Messenger of Allah (may Allah bless him and grant him peace) forbid the wearing of gold?" They said: "Yes." He said: "And I bear witness." He said: "I adjure you by Allah, did the Messenger of Allah (may Allah bless him and grant him peace) forbid the wearing of tiger skins?" They said: "Yes." He said: "And I bear witness."