Musannaf Ibn Abi Shayba 28:1

Waki’ ibn al-Jarrah narrated to us, he said: al-A’mash narrated to us, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever obeys me has obeyed Allah, and whoever obeys the Imam has obeyed me. And whoever disobeys me has disobeyed Allah, and whoever disobeys the Imam has disobeyed me."