Musannaf Ibn Abi Shayba 33:1492

Muhammad ibn Abd Allah al-Asadi narrated to us, from Sufyan, from Hisham, from his father, from Aisha: That she wrote to Muawiyah: "I advise you to fear Allah, for if you fear Allah, He will suffice you against the people. But if you fear the people, they will not avail you anything against Allah. So, you must fear Allah. Amma ba'd (as for what follows)."