Musannaf Ibn Abi Shayba 36:559

Waki’ narrated to us, from al-A’mash, from Abu Salih, who said: The camel driver used to sing to Uthman, saying: "Indeed, the leader after him is Ali, and in al-Zubayr is a successor." He said: So Ka’b said, "But he is the owner of the grey mule," meaning Mu’awiyah. It was said to Mu’awiyah, "Ka’b is mocking you and claims that you will govern this affair." He said: So he came to him and said, "O Abu Ishaq, how [could that be], when Ali, al-Zubayr, and the companions of Muhammad are here?" He said, "You are its owner."