Volume 4, Book 54, Number 446:
Narrated Abu Huraira:
The Prophet 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 over-night, ascent unto Allah Who asks them, and He knows
the answer better than they, “How have you left My slaves?” They reply, “We have left them praying
as we found them praying.” If anyone of you says “Amin” (during the Prayer at the end of the recita –
tion of Surat-al-Faitiha), and the angels in Heaven say the same, and the two sayings coincide, all his
past sins will be forgiven.”