Some of the companions of ʿAli ؓ said: Why donʿt you tell us about the voluntary prayers that the Messenger of Allah ﷺ offered during the day? ʿAli ؓ said: By Allah, you cannot do it. They said to him; Tell us about it and we will take whatever we are able to do... then he quoted the hadeeth at length. It was narrated from ‘Ali ؓ that He was asked about the (voluntary) prayers of the Messenger of Allah ﷺ during the day. He said: He used to pray sixteen rakʿahs, When the sun was as high there as it is at the time of ‘Asr there, he would pray two rak’ahs. When the sun was as high there as it is at the time of Zuhr there, he would pray two rakʿahs, He would pray four rakʿahs before Zuhr and two rakʿahs after Zuhr, and he would pray four rakʿahs before ʻAsr.  

نَاسٌ مِنْ أَصْحَابِ عَلِيٍّ لِعَلِيٍّ أَلَا تُحَدِّثُنَا بِصَلاةِ رَسُولِ اللهِ ﷺ بِالنَّهَارِ وَالتَّطَوُّعِ فَقَالَ عَلِيٌّ إِنَّكُمْ لَا تُطِيقُونَهَا فَقَالُوا لَهُ أَخْبِرْنَا بِهَا نَأْخُذْ مِنْهَا مَا أَطَقْنَا فَذَكَرَ الْحَدِيثَ بِطُولِهِ