[Machine] The Prophet ﷺ used to pray two units of prayer after Witr while sitting. In the first unit, he would recite Umm Al-Quran (Surah Al-Fatiha) and when he bowed, he would say "O Disbelievers." Abu Ghaleb and Utbah Ibn Abi Hakim reported this and it was narrated by Umara Bin Zadhan from Thabit from Anas regarding Witr - nine units then seven units. He would also pray two units while sitting, however, he would recite Al-Rahman and Al-Waqi'ah. Anas said, "And we would recite the short Surahs when they were revealed and 'O Disbelievers' and others like it."  

أَنَّ النَّبِيَّ ﷺ كَانَ يُصَلِّي بَعْدَ الْوِتْرِ الرَّكْعَتَيْنِ وَهُوَ جَالِسٌ يَقْرَأُ فِي الرَّكْعَةِ الْأُولَى بِأُمِّ الْقُرْآنِ وَإِذَا زُلْزِلَتْ وَفِي الثَّانِيَةِ قُلْ يَا أَيُّهَا الْكَافِرُونَ أَبُو غَالِبٍ وَعُتْبَةُ بْنُ أَبِي حَكِيمٍ غَيْرُ قَوِيَّيْنِ وَرَوَاهُ عُمَارَةُ بْنُ زَاذَانَ عَنْ ثَابِتٍ عَنْ أَنَسٍ فِي الْوِتْرِ بِتِسْعٍ ثُمَّ بِسَبْعٍ وَصَلَّى رَكْعَتَيْنِ وَهُوَ جَالِسٌ غَيْرَ أَنَّهُ قَالَ وَقَرَأَ فِيهِنَّ بِالرَّحْمَنِ وَالْوَاقِعَةِ قَالَ أَنَسٌ وَنَحْنُ نَقْرَأُ بِالسُّوَرِ الْقِصَارِ إِذَا زُلْزِلَتْ وَقُلْ يَا أَيُّهَا الْكَافِرُونَ وَنَحْوِهِمَا