Riyad Us-Saliheen (Gardens of the Righteous)

Chapter 181
Warning against forgetting the Qur'an

1002. Abu Musa Al-Ash`ari (May Allah be pleased with him) reported: The Prophet (PBUH) said, "Read the Qur'an regularly. By the One in Whose Hand Muhammad's soul is, it escapes from memory faster than a camel does from its tying ropes.''
[Al-Bukhari and Muslim].

Commentary:  To safeguard the Qur'an means to recite it regularly, because if one fails to do so, he tends to forget it quickly. In the absence of regular recitation, one is bound to forget it more quickly than a camel breaks loose bound with. The breaking loose by the camel to liberate itself is a simile for the quick process of forgetting.

1003. Ibn `Umar (May Allah be pleased with them) reported: The Messenger of Allah (PBUH) 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].

Commentary:  This Hadith repeats the subject mentioned above. The person who memorizes the entire Qur'an or a portion of it, if he recites it regularly, he will retain it; otherwise, it will start slipping from his memory.