The learning of the Qur'an by heart and the reciting of it repeatedly
حَدَّثَنَا مُحَمَّدُ بْنُ الْعَلاَءِ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ بُرَيْدٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِي مُوسَى، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " تَعَاهَدُوا الْقُرْآنَ فَوَالَّذِي نَفْسِي بِيَدِهِ لَهُوَ أَشَدُّ تَفَصِّيًا مِنَ الإِبِلِ فِي عُقُلِهَا ".
Narrated Abu Musa: The Prophet (ﷺ) said, "Commit yourself to the Qur'an, for by Him in whose Hand is my soul, it is surely more prone to break away than a camel in its bind.