Prophet (SAW)'s Prayers After Witr Prayer

Recite:

سُبْحَانَ الْمَلِكِ الْقُدُّوسِ

"I mention the Purity of the Owner, i.e. Allah who is Pure".

or read

اللَّهُمَّ إِنِّي أَعُوذُ بِرِضَاكَ مِنْ سَخَطِكَ وَبِمُعَافَاتِكَ مِنْ عُقُوبَتِكَ وَأَعُوذَ بِكَ مِنْكَ لَا أُحْصِي ثَنَاءً عَلَيْكَ أَنْتَ كَمَا أَثْنَيْتَ عَلَى نَفْسِكَ

"O Allah, I seek Your refuge (protection) from your displeasure through. Your pleasure and from Your punishment with forgiveness. I seek refuge from all calamities and punishments. I have no words to Praise You as You have praised Yourself. (Hisnul Hasin)