Ibn Mas’ūd 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’ān, for it is more apt to escape from men’s minds than animals.” (Bukhārī and Muslim, Muslim adding "which are tethered”.)
Hadith Referenceمشكوة المصابيح / كتاب فضائل القرآن / 2188
Hadith Gradingالألبانی:مُتَّفَقٌ عَلَيْهِ | زبیر علی زئی:متفق عليه
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «متفق عليه، رواه البخاري (5032) و مسلم (790/228)»