Sahih Bukhari Volume 6, Book 60, Hadith Number 241.

Narrated By Ibn Al-Musaiyab : Abu Huraira said, “The Prophet said, ‘A prayer performed in congregation is twenty-five times more superior in reward to a prayer performed by a single person. The angels of the night and the angels of the day are assembled at the time of the Fajr (Morning) prayer.” Abu Huraira added, “If you wish, you can recite: ‘Verily! The recitation of the Qur’an in the early dawn (Morning prayer) is ever witnessed (attended by the angels of the day and the night).’ (17.78)