"The Prophet would perform Witr with thirteen [Rak'ah]. When he was older and became weak he performed Witr with seven." (Using translation from Tirmidhī 457)
«كَانَ النَّبِيُّ ﷺ يُوتِرُ بِثَلَاثَ عَشْرَةَ فَلَمَّا كَبِرَ وَضَعُفَ أَوْتَرَ بِسَبْعٍ»