It is narrated from Sayyiduna Amr bin Salamah al-Jarmi (may Allah be pleased with him); he said: I went with my father to the Prophet (peace and blessings be upon him) with the news of our people's acceptance of Islam. Among the advice he (peace and blessings be upon him) gave us was: "Let the one of you who knows the most Qur'an lead you in prayer." Since I knew the most Qur'an among them, they put me forward.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14127