I know the similar surahs that the Messenger of Allah ﷺ used to recite, twenty surahs in ten rak'ahs." Then he took 'Alqamah's hand and went in, then 'Alqamah came out and we asked him and he told us what they were.  

إِنِّي لأَعْرِفُ النَّظَائِرَ الَّتِي كَانَ يَقْرَأُ بِهِنَّ رَسُولُ اللَّهِ ﷺ عِشْرِينَ سُورَةً فِي عَشْرِ رَكَعَاتٍ ثُمَّ أَخَذَ بِيَدِ عَلْقَمَةَ فَدَخَلَ ثُمَّ خَرَجَ إِلَيْنَا عَلْقَمَةُ فَسَأَلْنَاهُ فَأَخْبَرَنَا بِهِنَّ  

"I heard Abu Wa'il say: "A man said in the presence of Abdullah: 'I recited Al-Mufassal in one rak'ah.' He said: 'That is like reciting poetry. I know the similar surahs that the Messenger of Allah ﷺ used to recite together.' And he mentioned twenty surahs from Al-Mufassal, two by two in each rak'ah."  

رَجُلٌ عِنْدَ عَبْدِ اللَّهِ قَرَأْتُ الْمُفَصَّلَ فِي رَكْعَةٍ قَالَ هَذًّا كَهَذِّ الشِّعْرِ لَقَدْ عَرَفْتُ النَّظَائِرَ الَّتِي كَانَ رَسُولُ اللَّهِ ﷺ يَقْرُنُ بَيْنَهُنَّ فَذَكَرَ عِشْرِينَ سُورَةً مِنَ الْمُفَصَّلِ سُورَتَيْنِ سُورَتَيْنِ فِي رَكْعَةٍ  

A man came to him and said: "Last night I recited Al-Mufassal in one rak'ah." He said: "That is like reciting poetry. But the Messenger of Allah ﷺ used to recite similar surahs, twenty surahs from Al-Mufassal, those that start with Ha-Mim."  

إِنِّي قَرَأْتُ اللَّيْلَةَ الْمُفَصَّلَ فِي رَكْعَةٍ فَقَالَ هَذًّا كَهَذِّ الشِّعْرِ لَكِنَّ رَسُولَ اللَّهِ ﷺ كَانَ يَقْرَأُ النَّظَائِرَ عِشْرِينَ سُورَةً مِنَ الْمُفَصَّلِ مِنْ آلِ حم