Sahih Muslim Book - 4, Hadith - 1014

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى وَأَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ جَمِيعًا عَنْ هُشَيْمٍ قَالَ يَحْيَى أَخْبَرَنَا هُشَيْمٌ عَنْ مَنْصُورٍ عَنْ الْوَلِيدِ بْنِ مُسْلِمٍ عَنْ أَبِي الصِّدِّيقِ عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ كُنَّا نَحْزِرُ قِيَامَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي الظُّهْرِ وَالْعَصْرِ فَحَزَرْنَا قِيَامَهُ فِي الرَّكْعَتَيْنِ الْأُولَيَيْنِ مِنْ الظُّهْرِ قَدْرَ قِرَاءَةِ الم تَنْزِيلُ السَّجْدَةِ وَحَزَرْنَا قِيَامَهُ فِي الْأُخْرَيَيْنِ قَدْرَ النِّصْفِ مِنْ ذَلِكَ وَحَزَرْنَا قِيَامَهُ فِي الرَّكْعَتَيْنِ الْأُولَيَيْنِ مِنْ الْعَصْرِ عَلَى قَدْرِ قِيَامِهِ فِي الْأُخْرَيَيْنِ مِنْ الظُّهْرِ وَفِي الْأُخْرَيَيْنِ مِنْ الْعَصْرِ عَلَى النِّصْفِ مِنْ ذَلِكَ وَلَمْ يَذْكُرْ أَبُو بَكْرٍ فِي رِوَايَتِهِ الم تَنْزِيلُ وَقَالَ قَدْرَ ثَلَاثِينَ آيَةً

It was narrated that Abu Sa'eed Al-Khudri: said: "We estimated how long the Messenger of Allah (s.a.w) stood during Zuhr and 'Asr. We estimated that he stood during the first two Rak'ah of Zuhr for as long as it takes to recite ''Alif-Lam-Mim. The revelation of the Book..." We estimated that he stood in the last two Rak'ah for half that time. We estimated that he stood during the first two Rak'ah of 'Asr for as long as he stood during the last two Rak'ah of Zuhr, and we estimated that he stood during the last two Rak'ah for half of that." Abu Bakr did not mention ''Alif-Lam-Mim. The revelation of the Book..." in his Hadith, but he said: "As long as it takes to recite thirty Verses."