Is it obligatory to retrieve the forgotten surahs of the Qur’an due to negligence, and what if their forgetting recurs after re-memorization?

Forgetting the Qur’an is a reprehensible matter, and it may be a sin if it results from negligence and carelessness. It is obligatory for whoever forgets the Qur’an due to negligence to repent to Allah and try to recall what they memorized. If that is difficult, then there is no sin upon them. As for what is forgotten without negligence, there is no sin in it.