"Abu Dawud narrated to us, he said: Shu'ba narrated to us, from Qatadah, from Abdur-Rahman bin Abza, 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 said the taslim, he would say: Subhanal-Malikil-Quddus (Glory be to the Sovereign, the Most Holy) three times, elongating his words the third time." (Using translation from Nasāʾī 1741)  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ يُوتِرُ بِسَبِّحِ اسْمَ رَبِّكِ الْأَعْلَى وَقُلْ يَا أَيُّهَا الْكَافِرُونَ وَقُلْ هُوَ اللهُ أَحَدٌ فَإِذَا فَرَغَ قَالَ سُبْحَانَ الْمَلِكِ الْقُدُّوسِ ثَلَاثًا مَدَّ الصَّوْتَ بِالتَّسْبِيحِ فِي الثَّالِثَةِ  

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 رَسُولَ اللهِ ﷺ كَانَ يُوتِرُ بِسَبِّحِ اسْمَ رَبِّكَ الْأَعْلَى وَقُلْ يَا أَيُّهَا الْكَافِرُونَ وَقُلْ هُوَ اللهُ أَحَدٌ فَإِذَا سَلَّمَ قَالَ سُبْحَانَ الْمَلِكِ الْقُدُّوسِ ثَلَاثًا وَيَمُدُّهَا فِي الثَّالِثَةِ