Musannaf Ibn Abi Shayba 3:6012

Abu Bakr narrated to us, he said: Muhammad ibn Fudayl narrated to us, from ‘Ata’ ibn al-Sa’ib, from Abu al-Ahwas, from ‘Abdullah, that he heard the Messenger of Allah, may Allah bless him and grant him peace, saying: The superiority of a man’s prayer in congregation over his prayer alone is twenty-some degrees.