"The Messenger of Allah ﷺ used to pray witr with thirteen rak'ahs, but when he grew older and weaker he prayed witr with nine." (Using translation from Nasāʾī 1727)
كَانَ رَسُولُ اللهِ ﷺ «يُوتِرُ بِثَلَاثَ عَشْرَةَ رَكْعَةً فَلَمَّا كِبَرَ وَضَعُفَ أَوْتَرَ بِتِسْعٍ»