Does one sin if he memorizes part of the Qur'an and then forgets it?

Question:
May Allah reward you and bless you. This questioner says: Honorable Shaykh, what is the ruling on one who memorizes surahs from the Noble Qur'an and then forgets them? He has tried repeatedly to memorize them, but he forgets. What is your guidance for him, and does he sin?

Answer:
If the forgetting is due to his negligence and neglect, then that is something he should not do, because the Prophet (peace and blessings be upon him) commanded the review and recitation of the Qur'an, for it is more likely to slip away from the mind than a camel from its tether. However, if the forgetting is not due to any negligence on his part, but is the result of a weak memory or an illness that affected his memory, then he does not sin for it. Yes.