The command to keep refreshing one’s knowledge of the Qur’an and that it is disliked to say I have forgotten such-and-such a verse, but it is permissible to say I have been caused to forget Sahih Muslim 788 a
Translation
'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.