Abu Ali al-Misri narrates: We were travelling with Sayyiduna Uqbah bin Amir al-Juhani (may Allah be pleased with him) when the time of prayer came. We wanted him to go forward (and lead us). He said: I heard the Prophet (peace and blessings be upon him) say: "Whoever leads people in prayer, if he performs it completely, he will receive the complete reward and the people will also receive the complete reward; and if he (the imam) does not perform it completely, the people will receive the complete reward and the sin will be upon him (the imam)."
Ahmad recorded it, and al-Tabarani recorded part of it; its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2347