'A'isha reported that the Messenger of Allah (ﷺ) heard a person reciting the Qur'an at night. Upon this he said
May Allah show mercy to him; he has reminded me of such and such a verse which I had missed in such and such a surah.
'A'isha reported that the Messenger of Allah (ﷺ) listened to the recitation of the Qur'an by a man in the mosque. Thereupon he said
May Allah have mercy upon him; be reminded me of the verse which I had been made to forget.
'Abdullah b. 'Umar reported Allah's Messenger (ﷺ) as saying
The example of a man who has memorised the Qur'an is like that of a hobbled camel. If he remained vigilant, he would be able to retain it (with him), and if he loosened the hobbled camel it would escape.
This hadith has been narrated by Ibn 'Umar from the Messenger of Allah (ﷺ), but in the hadith transmited by Musa b. 'Uqba, this addition is made
" When one who had committed the Qur'an to memory (or who is familiar with it) gets up (for night prayer) and recites it night and day, it remains fresh in his mind, but if he does not get up (for prayer and thus does not recite it) he forgets it."
'Abdullah reported Allah's Messenger (ﷺ) as saying
What a wretched person is he amongst them who says: I have forgotten such and such a verse. (He should instead of using this expression say): I have been made to forget it. Try to remember the Qur'an for it is more apt to escape from men's minds than a hobbled camel.
'Abdullah is reported to have said
Keep refreshing your knowledge of the sacred books (or always renew your knowledge of these sacred books) and sometimes he would mention the Qur'an for it is more apt to escape from men's minds than animals which are hobbled, and the Messenger of Allah (ﷺ) said: None of you should say: I forgot such and such a verse, but he has been made to forget.
Ibn Mas'ud reported Allah's Messenger (ﷺ) as saying
Wretched is the man who says: I forgot such and such a sura, or I forget such and such a verse, but he has been made to forget.
Abu Musa al-Ash'ari reported Allah's Apostle (ﷺ) as saying
Keep refreshing your knowledge of the Qur'an, for I swear by Him in Whose Hand is the life of Mahammad that it is more liable to escape than camels which are hobbled.