Musannaf Ibn Abi Shayba 3:653

Hashim narrated to us, he said: Mughira informed us, from Ibrahim, who said: They used to like that the Imam would supplicate after the Tashahhud with five comprehensive phrases: "O Allah, we ask You for all good, what we know of it and what we do not know, and we seek refuge in You from all evil, what we know of it and what we do not know." He said: No matter how much the Imam hastens, do not hasten away from these words.