"The Messenger of Allah ﷺ used to recite in witr: Glorify the Name of Your Lord, the Most High;' and "Say: O you disbelievers!'; and 'Say: He is Allah, (the) One." And after he had said the salam, he would say: Subhanal-Malikil-Quddus (Glory be to the Sovereign, the Most Holy) three times, elongating the words the third time, then raising it." (Using translation from Nasāʾī 1753)  

كَانَ رَسُولُ اللهِ ﷺ يُوتِرُ بِسَبِّحِ اسْمَ رَبِّكَ الْأَعْلَى وَقُلْ يَا أَيُّهَا الْكَافِرُونَ وَقُلْ هُوَ اللهُ أَحَدٌ فَإِذَا سَلَّمَ قَالَ سُبْحَانَ الْمَلِكِ الْقُدُّوسِ ثَلَاثَ مَرَّاتٍ يَمُدُّ صَوْتَهُ فِي الثَّالِثَةِ وَيَرْفَعُ