Musnad Ahmad 30:2907

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, from Ya'la ibn 'Ata, he said: I heard Abu 'Alqamah saying: I heard Abu Hurairah saying: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "Whoever obeys me has obeyed Allah, and whoever disobeys me has disobeyed Allah. Whoever obeys the commander has obeyed me, and whoever disobeys the commander has disobeyed me." "The Imam is only a shield; so if he prays sitting, then pray sitting. And when he says: 'Allah hears those who praise Him,' then say: 'O Allah, our Lord, and to You is the praise.' For if the saying of the people of the earth coincides with the saying of the people of the heaven, his past sins will be forgiven."