Musnad Ahmad 30:3646

Narrated to us ‘Abd al-Malik ibn ‘Amr, narrated to us al-Mughirah, from Abu al-Zinad, from al-A‘raj, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him): "The Imam is only a shield; one fights from behind him and is protected by him. So if he commands the fear of Allah (taqwa) and justice, then he has a reward for that. And if he commands other than that, then upon him is the consequence of it."