Is a person sinful for forgetting four parts of the Noble Quran that he had memorized in his childhood before reaching puberty, and then forgot them after 20 years?

Forgetfulness is innate in humans, and the Quran slips away from hearts if a Muslim does not constantly review what they have memorized from it. Among the wisdoms behind this is testing, and encouraging the Muslim to recite the Quran frequently to earn reward, as the fear of forgetting motivates diligence in recitation. The Prophet, peace and blessings be upon him, urged the regular review of the Quran and warned against neglecting it. He likened the companion of the Quran to the owner of a tethered camel: if he looks after it, he keeps it, but if he releases it, it goes away. Similarly, if the companion of the Quran does not regularly review their memorization through repetition and revision, it will slip away from them. The notion that forgetting is a major sin was mentioned in a weak hadith, and the correct view is that it is not so for one who strives in revision. Among the greatest aids to remembering the Quran is to recite it in prayer and during prayer.