One of the Ansar used to lead the Ansar in Salat in the Quba' mosque and it was his habit to recite Qul Huwal-lahu Ahad whenever he wanted to recite something in Salat. When he finished that Surah, he would recite another one with it. He followed the same procedure in each Rak'a. His companions discussed this with him and said, "You recite this Surah and do not consider it sufficient and then you recite another. So would you recite it alone or leave it and recite some other." He said, "I will never leave it and if you want me to be your Imam on this condition then it is all right ; otherwise I will leave you." They knew that he was the best amongst them and they did not like someone else to lead them in Salat. When the Prophet ﷺ went to them as usual, they informed him about it. The Prophet ﷺ addressed him and said, "O so-and-so, what forbids you from doing what your companions ask you to do ? Why do you read this Surah particularly in every Rak'a ?" He repiled, "I love this Surah." The Prophet ﷺ said, "Your love for this Surah will make you enter Paradise."  

عَنْ أَنَسٍ ؓ كَانَ رَجُلٌ مِنَ الأَنْصَارِ يَؤُمُّهُمْ فِي مَسْجِدِ قُبَاءٍ وَكَانَ كُلَّمَا افْتَتَحَ سُورَةً يَقْرَأُ بِهَا لَهُمْ فِي الصَّلاَةِ مِمَّا يَقْرَأُ بِهِ افْتَتَحَ بِ {قُلْ هُوَ اللَّهُ أَحَدٌ} حَتَّى يَفْرُغَ مِنْهَا ثُمَّ يَقْرَأُ سُورَةً أُخْرَى مَعَهَا وَكَانَ يَصْنَعُ ذَلِكَ فِي كُلِّ رَكْعَةٍ فَكَلَّمَهُ أَصْحَابُهُ فَقَالُوا إِنَّكَ تَفْتَتِحُ بِهَذِهِ السُّورَةِ ثُمَّ لاَ تَرَى أَنَّهَا تُجْزِئُكَ حَتَّى تَقْرَأَ بِأُخْرَى فَإِمَّا أَنْ تَقْرَأَ بِهَا وَإِمَّا أَنْ تَدَعَهَا وَتَقْرَأَ بِأُخْرَى فَقَالَ مَا أَنَا بِتَارِكِهَا إِنْ أَحْبَبْتُمْ أَنْ أَؤُمَّكُمْ بِذَلِكَ فَعَلْتُ وَإِنْ كَرِهْتُمْ تَرَكْتُكُمْ وَكَانُوا يَرَوْنَ أَنَّهُ مِنْ أَفْضَلِهِمْ وَكَرِهُوا أَنْ يَؤُمَّهُمْ غَيْرُهُ فَلَمَّا أَتَاهُمُ النَّبِيُّ ﷺ أَخْبَرُوهُ الْخَبَرَ فَقَالَ يَا فُلاَنُ مَا يَمْنَعُكَ أَنْ تَفْعَلَ مَا يَأْمُرُكَ بِهِ أَصْحَابُكَ وَمَا يَحْمِلُكَ عَلَى لُزُومِ هَذِهِ السُّورَةِ فِي كُلِّ رَكْعَةٍ فَقَالَ إِنِّي أُحِبُّهَا فَقَالَ حُبُّكَ إِيَّاهَا أَدْخَلَكَ الْجَنَّةَ  

A man came to Ibn Masʿud and said, "I recited the Mufassal (Suras) at night in one rakʿa." Ibn Masʿud said, "This recitation is (too quick) like the recitation of poetry. I know the identical Suras which the Prophet ﷺ used to recite in pairs." Ibn Masʿud then mentioned 20 Mufassal Suras including two Suras from the family of (i.e. those verses which begin with) Ha, Meem [??] (which the Prophet ﷺ used to recite) in each rakʿa.  

هَذًّا كَهَذِّ الشِّعْرِ لَقَدْ عَرَفْتُ النَّظَائِرَ الَّتِي كَانَ النَّبِيُّ ﷺ يَقْرِنُ بَيْنَهُنَّ فَذَكَرَ عِشْرِينَ سُورَةً مِنَ الْمُفَصَّلِ سُورَتَيْنِ فِي كُلِّ رَكْعَةٍ