It was narrated from Abdullah that:The Prophet (ﷺ) said: "It is not right for any one of you to say: 'I have forgotten such and such a verse.' Rather, he has been caused to forget. Study the Qur'an, for it escapes from the heart of man faster than a camel escapes from its fetter. "
أَخْبَرَنَا عِمْرَانُ بْنُ مُوسَى، قَالَ حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ مَنْصُورٍ، عَنْ أَبِي وَائِلٍ، عَنْ عَبْدِ اللَّهِ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " بِئْسَمَا لأَحَدِهِمْ أَنْ يَقُولَ نَسِيتُ آيَةَ كَيْتَ وَكَيْتَ بَلْ هُوَ نُسِّيَ اسْتَذْكِرُوا الْقُرْآنَ فَإِنَّهُ أَسْرَعُ تَفَصِّيًا مِنْ صُدُورِ الرِّجَالِ مِنَ النَّعَمِ مِنْ عُقُلِهِ ".
Nesai
The Book of the Commencement of the Prayer • Hadith 943