When he finished the prayer, the Messenger of Allah ﷺ would pray for forgiveness three times and say: O Allah, You are the source of eace (or the One free from all faults) and from You comes peace, blessed are You, O Possessor of Majesty and Honor.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا انْصَرَفَ مِنْ صَلاَتِهِ اسْتَغْفَرَ ثَلاَثًا وَقَالَ اللَّهُمَّ أَنْتَ السَّلاَمُ وَمِنْكَ السَّلاَمُ تَبَارَكْتَ يَا ذَا الْجَلاَلِ وَالإِكْرَامِ