After the prayer, O Allah, You are Peace
Sahihاللَّهُمَّ أَنْتَ السَّلاَمُ وَمِنْكَ السَّلاَمُ تَبَارَكْتَ ذَا الْجَلاَلِ وَالإِكْرَامِ
Allāhumma anta as-salām wa minka as-salām, tabārakta yā dhal-jalāli wal-ikrām.
O Allah, You are Peace and from You comes peace. Blessed are You, Owner of majesty and honour.
Note: Before it the Prophet ﷺ sought forgiveness three times; al-Awzāʿī explained this as saying astaghfirullāh, astaghfirullāh.