Musnad Ahmad 482:15

Al-Hakam ibn Nafi’ narrated to us, he said: Ibn ‘Ayyash narrated to us, from ‘Abd al-Rahman ibn Harmalah al-Aslami, from Abu ‘Ali al-Hamdani, who said: I went out on a journey, and ‘Uqbah ibn ‘Amir was with us. He said: We said to him, "May Allah have mercy on you, you are one of the companions of the Messenger of Allah, peace and blessings of Allah be upon him, so lead us in prayer." He said: "No, for I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'Whoever leads the people in prayer and hits the time, and completes the prayer, then it is for him and for them. And whoever falls short of that in any way, then it is upon him and not upon them.'"