Sahih al-Bukhari, Volume 6, Book 61, Hadith 552 (USC-MSA) ⓘ
Narrated Abu Musa: The Prophet said, "Keep on reciting the Qur'an, for, by Him in Whose Hand my life is, Qur'an runs away (is forgotten) faster than camels that are released from their tying ropes."
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 " .
also referenced under: Book 66, Hadith 56 (In-Book) & Hadith 5033 (DarusSalam)