The end of the prayer of the Messenger of Allah ﷺ was known by the takbir (pronounced aloud).  

كَانَ يُعْلَمُ انْقِضَاءُ صَلاَةِ رَسُولِ اللَّهِ ﷺ بِالتَّكْبِيرِ  

To raise the voice for making the mention of Allah after the people had finished their obligatory prayer was for in vogue the time of the Messenger of Allah (May peace be upon him). Ibn ‘Abbas said : I used to know by it when they finished the prayer and would listen to it (making the mention of Allah).  

أَخْبَرَهُ أَنَّ رَفْعَ الصَّوْتِ لِلذِّكْرِ حِينَ يَنْصَرِفُ النَّاسُ مِنَ الْمَكْتُوبَةِ كَانَ ذَلِكَ عَلَى عَهْدِ رَسُولِ اللَّهِ ﷺ وَأَنَّ ابْنَ عَبَّاسٍ قَالَ كُنْتُ أَعْلَمُ إِذَا انْصَرَفُوا بِذَلِكَ وَأَسْمَعُهُ