Musnad Abu Ya'la al-Mawsili 138:5

Ishaq ibn Abi Isra'il narrated to us, Abd al-Samad narrated to us, Harb narrated to us, Yahya narrated to us, Amr ibn Zaynab narrated to me, that Anas ibn Malik narrated to him, that Mu'adh said: "O Messenger of Allah, what is your opinion if we have leaders who do not follow your Sunnah and do not take by your command? So what do you command me regarding their affair?" The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no obedience for one who does not obey Allah."