Musannaf Ibn Abi Shayba 24:182

Ibn Numayr narrated to us, from Isma'il ibn Ibrahim, from 'Abd al-Malik ibn 'Umayr, who said: Mu'awiyah said: "I never ceased to covet the Caliphate since the Messenger of Allah, may Allah bless him and grant him peace, said to me: 'O Mu'awiyah, if you come to rule, then do good.'"