صَحِيحُ مُسْلِمٍ
Sahih Muslim 790 a
The Book of Prayer - Travellers
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
وَحَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، وَعُثْمَانُ بْنُ أَبِي شَيْبَةَ، وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ إِسْحَاقُ أَخْبَرَنَا وَقَالَ الآخَرَانِ، حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ أَبِي وَائِلٍ، عَنْ عَبْدِ اللَّهِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِئْسَمَا لأَحَدِهِمْ يَقُولُ نَسِيتُ آيَةَ كَيْتَ وَكَيْتَ بَلْ هُوَ نُسِّيَ اسْتَذْكِرُوا الْقُرْآنَ فَلَهُوَ أَشَدُّ تَفَصِّيًا مِنْ صُدُورِ الرِّجَالِ مِنَ النَّعَمِ بِعُقُلِهَا .
'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.
Sahih Muslim, 790 aSahihصحيح