It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: The superiority of praying in congregation over praying alone is twenty-five degrees. And the angels of the night and the day gather at the time of Fajr prayer. Then Hazrat Abu Huraira (may Allah be pleased with him) said: If you wish, you may recite this verse in confirmation of it: "Indeed, the recitation of the Qur'an at Fajr is witnessed." (At that time, the angels bear witness because they are present then.)
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 7612