´Narrated 'Abdullah:` that the Prophet (ﷺ) said: "How horrible it is for one of them - or - one of you to say: "I have forgotten such and such Ayah,' rather he was made to forget. So be mindful of the Qur'an, for - by the One in Whose Hand is my soul - it escapes from men's hearts faster than a camel from its fetter."
Hadith Referenceسنن ترمذي / كتاب القراءات عن رسول الله صلى الله عليه وسلم / 2942