It is narrated from Sayyiduna Uthman bin Affan (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever offers the Isha prayer in congregation, it is as if he stood in prayer for half the night, and whoever offers the Fajr prayer in congregation, it is as if he stood in prayer for the whole night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2178