Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "The people should be led in prayer by the one who has the most knowledge of the Qur'an." (Or: the one who has memorised the most of the Qur'an.)
Ahmad recorded it, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2318