"Abu Dawud narrated to us from Shu'bah, from Qatadah, who said: I heard 'Azarah narrating from Sa'eed bin 'Abdur-Rahman Ibn Abza, from his father That 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 had finished praying, he said: Subhanal-Malikil-Quddus (Glory be to the Sovereign, the Most Holy) three times." (Using translation from Nasāʾī 1740)
أَنَّ رَسُولَ اللهِ ﷺ كَانَ يُوتِرُ بِسَبِّحِ اسْمَ رَبِّكَ الْأَعْلَى وَقُلْ يَا أَيُّهَا الْكَافِرُونَ وَقُلْ هُوَ اللهُ أَحَدٌ فَإِذَا فَرَغَ قَالَ «سُبْحَانَ الْمَلِكِ الْقُدُّوسِ» ثَلَاثًا