Ibn 'Umar (May Allah be pleased with them) reported:
The Messenger of Allah ﷺ said: "The parable of one who knows the Qur'an by heart is as the parable of an owner of hobbled camel. If he remains vigilant, he will retain it; and if he neglects it, it will go away."

[Al-Bukhari and Muslim].

وعن ابن عمر رضي الله عنهما أن رسول الله ﷺ قال: "إنما مثل صاحب القرآن كمثل الإبل المعقلة، إن عاهد عليها أمسكها، وإن أطلقها، ذهبت" متفق عليه.