مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3455
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
‘Amr bin Dinar narrated that Abu Ma'bad, the freed slave of Ibn 'Abbas, told him that Ibn ‘Abbas (رضي الله عنه) told him that Raising the voice in dhikr when the people have finished the obligatory prayer was done at the time of the Prophet (ﷺ), and that he said: Ibn ‘Abbas (رضي الله `عنه) said: I would know that they had finished (the prayer) when I heard that.
Musnad Ahmad 3478Its isnad is saheeh, al-Bukhari (841) and Muslim (583)]