وَعَنِ ابْنِ مَسْعُودٍ
قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «بئس مالأحدهم أَنْ يَقُولَ: نَسِيتُ آيَةَ كَيْتَ وَكَيْتَ بَلْ نُسِّيَ وَاسْتَذْكِرُوا الْقُرْآنَ فَإِنَّهُ أَشَدُّ تَفَصِّيًا مِنْ صُدُورِ الرِّجَالِ مِنَ النَّعَمِ»
Ibn Masud reported God’s messenger as saying, “It is wrong for one to say that he has forgotten such and such a verse, for he has been made to forget. Study the Qur’an, for it is more apt to escape from men’s minds than animals.” (Bukhari and Muslim, Muslim adding “which are tethered”.)
Mishkat al-Masabih 2092, Book 9, The Excellent Qualities of the Qur'an, Hadith 78. 1 min read