Language:
كتاب فضائل القرآن
66
Virtues of the Qur'an
(23)
Chapter: The learning of the Qur'an by heart and the reciting of it repeatedly
(23)
باب اسْتِذْكَارِ الْقُرْآنِ وَتَعَاهُدِهِ

Narrated Ibn `Umar:

Allah's Messenger (ﷺ) said, "The example of the person who knows the Qur'an by heart is like the owner of tied camels. If he keeps them tied, he will control them, but if he releases them, they will run away."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ إِنَّمَا مَثَلُ صَاحِبِ الْقُرْآنِ كَمَثَلِ صَاحِبِ الإِبِلِ الْمُعَقَّلَةِ إِنْ عَاهَدَ عَلَيْهَا أَمْسَكَهَا وَإِنْ أَطْلَقَهَا ذَهَبَتْ ‏"‏‏.‏
Reference : Sahih al-Bukhari 5031
In-book reference : Book 66, Hadith 53
USC-MSA web (English) reference : Vol. 6, Book 61, Hadith 549
  (deprecated numbering scheme)