The Tasbih after finishing witr and the variance reported from Sufyan about that
أَخْبَرَنَا أَحْمَدُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا قَاسِمٌ، عَنْ سُفْيَانَ، عَنْ زُبَيْدٍ، عَنْ سَعِيدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ أَبْزَى، عَنْ أَبِيهِ، عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ كَانَ يُوتِرُ بِـ { 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 .
It was narrated from Ibn Abdur-Rahman bin 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 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."