[Machine] The Prophet ﷺ used to pray eight units of prayer and then he would perform the Witr prayer as the ninth. But when he grew older, he prayed six units, performed the Witr prayer as the seventh, and then prayed two units while sitting.
أَنَّ النَّبِيَّ ﷺ كَانَ «يُصَلِّي ثَمَانِيَ رَكَعَاتٍ وَيُوتِرُ بِالتَّاسِعَةِ فَلَمَّا بَدُنَ صَلَّى سِتَّ رَكَعَاتٍ وَأَوْتَرَ بِالسَّابِعَةِ وَصَلَّى رَكْعَتَيْنِ وَهُوَ جَالِسٌ»
The Messenger of Allah ﷺ used to pray thirteen rak'ahs during the night, observing the witr prayer with nine (or as she said). He used to pray two rak'ahs while sitting and pray two rak'ahs of the dawn prayer between the adhan and the iqamah.
أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يُصَلِّي مِنَ اللَّيْلِ ثَلاَثَ عَشْرَةَ رَكْعَةً يُوتِرُ بِسَبْعٍ أَوْ كَمَا قَالَتْ وَيُصَلِّي رَكْعَتَيْنِ وَهُوَ جَالِسٌ وَرَكْعَتَىِ الْفَجْرِ بَيْنَ الأَذَانِ وَالإِقَامَةِ