Virtue of saying Amin with the Imam

Friday - Hadeeth of the week (Book of Invocation)

Collected from Sahih Bukhari
Volume 8, Book 75, Number 411:

Narrated Abu Huraira:

The Prophet said, "When the Imam says 'Amin', then you should all say 'Amin', for the angels say 'Amin' at that time, and he whose 'Amin' coincides with the 'Amin' of the angels, all his past sins will be forgiven."