Narrated Ibn `Abbas: I used to recognize the completion of the prayer of the Prophet by hearing Takbir.

Narrated Abu Ma`bad: (the freed slave of Ibn `Abbas) Ibn `Abbas told me, "In the lifetime of the Prophet it was the custom to celebrate Allah's praises aloud after the compulsory congregational prayers." Ibn `Abbas further said, "When I heard the Dhikr, I would learn that the compulsory congregational prayer had ended."