Sahih Muslim
Sahih Muslim 788 a
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
Arabic hadith text
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَأَبُو كُرَيْبٍ قَالاَ حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم سَمِعَ رَجُلاً يَقْرَأُ مِنَ اللَّيْلِ فَقَالَ "يَرْحَمُهُ اللَّهُ لَقَدْ أَذْكَرَنِي كَذَا وَكَذَا آيَةً كُنْتُ أَسْقَطْتُهَا مِنْ سُورَةِ كَذَا وَكَذَا "
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.