Musnad Ahmad 482:33

Ishaq ibn Isa narrated to us, he said: Attaf narrated to us, from Abd al-Rahman ibn Harmalah, from a man from Juhaynah, from Uqbah ibn Amir, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "There will be leaders over you after me. If they perform the prayer at its time, then complete the bowing and the prostration, for it is for you and for them. But if they do not perform the prayer at its time, and do not complete its bowing or its prostration, then it is for you and against them."