Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Praying in congregation is superior to a man's praying alone by twenty-five degrees."
Imam al-Bazzar recorded it, and Imam al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains a narrator, Abd al-Hakim bin Mansur, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2139