[Machine] That the Prophet ﷺ used to perform voluntary prayers of nine units, but when he grew older and weaker, he would perform the voluntary prayers of seven units.
أَنَّ النَّبِيَّ ﷺ كَانَ «يُوتِرُ بِتِسْعٍ فَلَمَّا أَسَنَّ وَثَقُلَ أَوْتَرَ بِسَبْعٍ»