Ubayy bin Ka'b said: "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 when he said the salam, he would say: Subhanal-Malikil-Quddus (Glory be to the Sovereign, the Most Holy) three times." (Using translation from Nasāʾī 1729)
أَنَّ النَّبِيَّ ﷺ كَانَ يَقْرَأُ فِي الْوِتْرِ بِسَبِّحِ اسْمَ رَبِّكَ الْأَعْلَى وَقُلْ يَا أَيُّهَا الْكَافِرُونَ وَقُلْ هُوَ اللهُ أَحَدٌ فَإِذَا سَلَّمَ قَالَ سُبْحَانَ الْمَلِكِ الْقُدُّوسِ ثَلَاثَ مَرَّاتٍ يَرْفَعُ بِالثَّالِثَةِ صَوْتَهُ