Musnad Ahmad 1202, 1203
It was narrated that `Asim bin Damrah said:
Some of the companions of `Ali (رضي الله عنه) said: Why don`t you tell us about the voluntary prayers that the Messenger of Allah (ﷺ) offered during the day? `Ali  (رضي الله عنه) 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 (رضي الله عنه) that He was asked about the (voluntary) prayers of the Messenger of Allah (ﷺ)  during the day. He said: He used to pray sixteen rak`ahs, 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 rak`ahs, He would pray four rak`ahs before Zuhr and two rak`ahs after Zuhr, and he would pray four rak`ahs before ʻAsr.
حَدَّثَنَا عَبْد اللَّهِ، حَدَّثَنِي أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو الْأَحْوَصِ، عَنْ أَبِي إِسْحَاقَ، عَنْ عَاصِمِ بْنِ ضَمْرَةَ، قَالَ قَالَ نَاسٌ مِنْ أَصْحَابِ عَلِيٍّ لِعَلِيٍّ رَضِيَ اللَّهُ عَنْهُ أَلَا تُحَدِّثُنَا بِصَلَاةِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِالنَّهَارِ وَالتَّطَوُّعِ فَقَالَ عَلِيٌّ رَضِيَ اللَّهُ عَنْهُ إِنَّكُمْ وَاللَّهِ لَا تُطِيقُونَهَا فَقَالُوا لَهُ أَخْبِرْنَا بِهَا نَأْخُذْ مِنْهَا مَا أَطَقْنَا فَذَكَرَ الْحَدِيثَ بِطُولِهِ.
حَدَّثَنَا عَبْد اللَّهِ حَدَّثَنَا أَبُو كَامِلٍ الْجَحْدَرِيُّ فُضَيْلُ بْنُ الْحُسَيْنِ إِمْلَاءً عَلَيَّ مِنْ كِتَابِهِ حَدَّثَنَا أَبُو عَوَانَةَ عَنْ أَبِي إِسْحَاقَ عَنْ عَاصِمِ بْنِ ضَمْرَةَ عَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ أَنَّهُ سُئِلَ عَنْ صَلَاةِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِالنَّهَارِ فَقَالَ كَانَ يُصَلِّي سِتَّ عَشْرَةَ رَكْعَةً قَالَ يُصَلِّي إِذَا كَانَتْ الشَّمْسُ مِنْ هَاهُنَا كَهَيْئَتِهَا مِنْ هَاهُنَا كَصَلَاةِ الْعَصْرِ رَكْعَتَيْنِ وَكَانَ يُصَلِّي إِذَا كَانَتْ الشَّمْسُ مِنْ هَاهُنَا كَهَيْئَتِهَا مِنْ هَاهُنَا كَصَلَاةِ الظُّهْرِ أَرْبَعَ رَكَعَاتٍ وَكَانَ يُصَلِّي قَبْلَ الظُّهْرِ أَرْبَعَ رَكَعَاتٍ وَبَعْدَ الظُّهْرِ رَكْعَتَيْنِ وَقَبْلَ الْعَصْرِ أَرْبَعَ رَكَعَاتٍ‏.‏