Musnad Ahmad 547:6

'Ali ibn 'Asim narrated to us, he said: 'Abd al-Rahman ibn Harmalah narrated to me, from Abu 'Ali al-Hamdani, who said: We accompanied 'Uqbah ibn 'Amir on a journey, and he would not lead us in prayer. We said to him: "May Allah have mercy on you, will you not lead us in prayer, while you are one of the companions of Muhammad, may Allah bless him and grant him peace?" He said: "No, for I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'Whoever leads the people in prayer and hits the time correctly, and completes the prayer, then it is for him and for them. And whoever falls short of that, then it is upon him and not upon them.'"