The Prophet SA said, “Angels keep on descending

The Prophet صلى الله عليه وسلم said, “Angels keep on descending from and ascending to the heaven in turn, some at night and some by daytime, and all of them assemble together at the time of the Fajr and ‘Asr prayers. Then those who have stayed with you overnight, ascend unto Allah Who asks them (and He knows the answer better than they): “How have you left My slaves?” They reply, “We left them while they were praying and we came to them while they were praying.” The narrator added: “If anyone of you says ‘Amin (during the prayer at the end of the recitation of Surat Al-Fatiha), and the angels in heaven say the same, and the two sayings coincide, all his past sins will be forgiven.”

Bukhari, Vol. 4, Hadith No. 446, Narrated by Abu Huraira