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) raising his voice the third time."
عَنِ النَّبِيِّ ﷺ أَنَّهُ كَانَ يُوتِرُ بِ { سَبِّحِ اسْمَ رَبِّكَ الأَعْلَى } وَ { قُلْ يَا أَيُّهَا الْكَافِرُونَ } وَ { قُلْ هُوَ اللَّهُ أَحَدٌ } وَيَقُولُ بَعْدَ مَا يُسَلِّمُ سُبْحَانَ الْمَلِكِ الْقُدُّوسِ ثَلاَثَ مَرَّاتٍ يَرْفَعُ بِهَا صَوْتَهُ