Yahya related to me from Malik from Nafi from Abdullah ibn Umarthat the Messenger of Allah, may Allah bless him and grant him peace,said, "Prayer in congregation is better than the prayer of a man byhimself by twenty-seven degrees."
App reference: Book 8, Hadith 1
USC-MSA web (English) reference: Book 8, Hadith 1
Arabic reference: Book 8, Hadith 288