Musnad Ahmad 62:0

It was narrated from a man among the chiefs of Quraysh, who said: I heard the Messenger of Allah (ﷺ) say: "The Imam is a shield, behind whom they fight and by whom they are protected. If he commands the fear of Allah, the Mighty and Majestic, and acts justly, he will have a reward for that. But if he commands otherwise, it will be against him."