Muwatta Malik 475

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ إِنَّمَا مَثَلُ صَاحِبِ الْقُرْآنِ كَمَثَلِ صَاحِبِ الإِبِلِ الْمُعَقَّلَةِ إِنْ عَاهَدَ عَلَيْهَا أَمْسَكَهَا وَإِنْ أَطْلَقَهَا ذَهَبَتْ ‏"‏ ‏.‏

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "A man who knows the Qur'an well is like a man who has a hobbled camel. If he takes care of it, he keeps it, and if he lets it go, it gets away

Reference

Muwatta Malik 475

In-book

Book 15, Hadith 6