Musnad Ahmad 210:1

'Ali ibn 'Asim narrated to us, Khalid al-Hadhdha' said: He informed me from Abu Qilabah, from 'Amr ibn Salamah, who said: The riders used to come to us from the direction of the Messenger of Allah, may Allah bless him and grant him peace, and we would ask them to recite [the Quran to us]. They would tell us that the Messenger of Allah, may Allah bless him and grant him peace, said: "Let the one among you who has the most Quran lead you in prayer."