"The Messenger of Allah ﷺ used to pray witr with nine rak'ahs, then he would pray two rak'ahs sitting down. When he grew weaker he prayed witr with seven rak'ahs, then he prayed two rak'ahs sitting down." (Using translation from Nasāʾī 1722)  

أَنَّهُ سَمِعَهَا تَقُولُ إِنَّ رَسُولَ اللهِ ﷺ كَانَ «يُوتِرُ بِتِسْعِ رَكَعَاتٍ ثُمَّ يُصَلِّي رَكْعَتَيْنِ وَهُوَ جَالِسٌ فَلَمَّا ضَعُفَ أَوْتَرَ بِسَبْعِ رَكَعَاتٍ ثُمَّ يُصَلِّي رَكْعَتَيْنِ وَهُوَ جَالِسٌ»