Musannaf Ibn Abi Shayba 24:176

Aswad ibn Amir narrated to us, he said: Jarir ibn Hazim narrated to us, he said: I heard Muhammad ibn Sirin say: Ali ibn Abi Talib sent Qays ibn Sa’d as a commander over Egypt. He said: Mu’awiyah and Amr ibn al-As wrote a letter to him, in which they were harsh toward him, insulted him, and threatened him. So he wrote a letter back to them, in order to provoke them and make them covet him for himself. He said: When the letter reached them, they wrote a letter to him mentioning his virtue and making him covet what was with them. So he wrote back to them with a response to their first letter, being harsh, and he did not leave anything out without saying it. One of them said to the other: "No, by Allah, we cannot handle Qays ibn Sa’d. But come, let us plot against him with Ali." He said: So they sent his first letter to Ali. He said: The people of Kufa said to him: "The enemy of Allah, Qays ibn Sa’d, so dismiss him." Ali said: "Woe to you, I, by Allah, know better; it is one of his tricks." But they insisted on his dismissal, so he dismissed him and sent Muhammad ibn Abi Bakr. When he arrived, Qays ibn Sa’d said to him: "Look at what I command you to do. When Mu’awiyah writes to you such and such, then write to him such and such. And when he does such and such, then do such and such. And beware of disobeying what I have commanded you to do. By Allah, it is as if I am looking at you; if you do [otherwise], you will be killed, then placed inside the belly of a donkey, then burned with fire." He said: And that is what was done to him.