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 790 c
Translation
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.