Musnad Ahmad 25:1619

'Abd al-Razzaq and Ibn Bakr narrated to us, they said: Ibn Jurayj informed us, he said: 'Amr ibn Dinar informed me, that Abu Ma'bad, the freed slave of Ibn 'Abbas, informed him that Ibn 'Abbas informed him: That "raising the voice with the dhikr when the people depart from the prescribed prayer was [the practice] during the time of the Prophet, may Allah bless him and grant him peace." And he said: Ibn 'Abbas said: "I would know when they had departed by that [sound] when I heard it."