The Prophet ﷺ said, "How wretched it is for one of you to say, 'I have forgotten such-and-such a verse.' Rather, he was made to forget. Keep reviewing the Quran, for it slips away from the hearts of Some men faster than livestock escape from their tethers."
أخبرنا عمران بن موسى قال حدثنا يزيد بن زريع قال حدثنا شعبة عن منصور عن أبي وائل
عن النبي ﷺ قال بئسما لأحدهم أن يقول نسيت آية كيت وكيت بل هو نسي استذكروا القرآن فإنه أسرع تفصيا من صدور الرجال من النعم من عقله
Bukhari narrated it in the Book of the Excellences of the Quran, in the chapter on reviewing and maintaining familiarity with the Quran, hadith no. 5032, from the hadith of Shubah, and Muslim narrated it in the Book of the Prayer of Travelers, in the chapter on the command to maintain familiarity with the Quran, etc., hadith no. 790, from the hadith of Mansur, through him, and it is also in Al-Kubra, hadith no. 1015.