Sahih Bukhari Volume 1, Book 12, Hadith Number 802

Narated By 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.”