Musnad Abu Ya'la al-Mawsili 159:24

Abu Khaythama narrated to us, Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, 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 my commander has obeyed me."