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. " (Using translation from Nasāʾī 943)  

عَنِ النَّبِيِّ ﷺ قَالَ بِئْسَمَا لِأَحَدِكُمْ أَنْ يَقُولَ نَسِيتُ آيَةَ كَيْتَ وَكَيْتَ بَلْ هُوَ نُسِّيَ فَاسْتَذْكِرُوا الْقُرْآنَ فَإِنَّهُ أَسْرَعُ تَفَصِّيًا مِنْ صُدُورِ الرِّجَالِ مِنَ النَّعَمِ مِنْ عُقُلِهَا