Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "The people should be led in prayer by the one who has the most knowledge of the Book of Allah Almighty (i.e. who has memorised the most of it)."
Al-Bazzar recorded it; its chain contains al-Hasan bin Ali al-Nawfali al-Hashimi, who is da'if (weak), though al-Bazzar declared it hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2321