"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."  

كَانَ رَسُولُ اللَّهِ ﷺ يُوتِرُ بِثَلاَثَ عَشْرَةَ رَكْعَةً فَلَمَّا كَبِرَ وَضَعُفَ أَوْتَرَ بِتِسْعٍ