It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him); he said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Prayer in congregation surpasses a man's prayer alone by twenty-four degrees, meaning that in comparison with his single (solitary) prayer, (the congregational prayer) receives the reward of twenty-five prayers."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4917