Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) says: I heard the Prophet (peace and blessings be upon him) say: "Indeed, Allah Almighty is pleased with the offering of prayer in congregation."
Imam Ahmad recorded it, and its chain is hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2140