The Prophet (ﷺ) used to recite this dhikr three times at the end of the Witr prayer, and the last time he would say it at length:
سُبْحَانَ الْمَلِكِ الْقُّدُّوْسِ
سُبْحَانَ الْمَلِكِ الْقُّدُّوْسِ
Subhaanal-Malikil-Quddoos
Glory is to the King, the Holy.
The Messenger of Allah (ﷺ) used to say towards the end of Witr prayer:
اَللَّهُمَّ إِنِّي أَعُوْذُ بِرِضَاكَ مِنْ سَخَطِكَ، وَبِمُعَافَاتِكَ مِنْ عُقُوبَتِكَ، وَأَعُــوذُ بِكَ مِنْكَ، لَا أُحْصِيْ ثَنَاءً عَلَيْكَ، أَنْتَ كَمَا أَثْنَيْتَ عَلَى نَفْسِكَ
اَللّٰهُمَّ اِنِّيْ اَعُوْذُ بِرِضَاكَ مِنْ سَخَطِكَ، وَبِمُعَافَاتِكَ مِنْ عُقُوْبَتِكَ، وَاَعُوْذُ بِكَ مِنْكَ، لَا اُحْصِيْ ثَنَاءً عَلَيْكَ، اَنْتَ كَمَا اَثْنَيْتَ عَلٰى نَفْسِكَ
Allaahumma 'innee 'a'oodhu biridhaaka min sakhatik, wa bimu'aafaatika min 'uqoobatik wa 'a'oodhu bika minka, laa 'uhsee thanaa'an 'alayka 'Anta kamaa 'athnayta 'alaa nafsik
O Allah, I seek refuge with Your Pleasure from Your anger. I seek refuge in Your forgiveness from Your punishment. I seek refuge in You from You. I cannot count Your praises, You are as You have praised Yourself.
Ali (RA) said, Rasulullah (ﷺ) used to say the words at the end of Witr prayer. The end of Witr prayer here is not clearly stated before the salaam or after the salaam. Therefore, a believer can recite this dua at the end of Salatul Witr prayer before Salaam or after Salaam.
The last time he extended his voice, he said -
رَبُّ الْمَلَائِكَةِ وَالرُّوحِ
رَبُّ الْمَلَائِكَةِ وَالرُّوْحِ
Rabbul-malaa'ikati warrooh
Lord of the angels and the Spirit.
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