Slow, measured pace of recitation (tartil), and to not rush when reciting, and the permissibility of reciting two or more surahs in one rak`ah Sahih Muslim 822 c
وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا عِيسَى بْنُ يُونُسَ، حَدَّثَنَا الأَعْمَشُ، فِي هَذَا الإِسْنَادِ . بِنَحْوِ حَدِيثِهِمَا وَقَالَ إِنِّي لأَعْرِفُ النَّظَائِرَ الَّتِي كَانَ يَقْرَأُ بِهِنَّ رَسُولُ اللَّهِ صلى الله عليه وسلم اثْنَتَيْنِ فِي رَكْعَةٍ . عِشْرِينَ سُورَةً فِي عَشْرِ رَكَعَاتٍ .
Translation
This hadith has been narrated by A'mash with the same chain of transmitters in which ('Abdullah b. Mas'ud) said
" I know the manners in which the Messenger of Allah (ﷺ) recited the two surahs in one rak'ah and then twenty surahs in ten rak'ahs."