Is forgetting the Quran after memorizing it considered abandoning it? And will the Quran be a proof against its owner if he memorizes it and then forgets it? And does this fall under the category of showing off?

To preserve the Noble Qur’an, it is essential to review it, care for it, reflect upon it, and recite it frequently. Memorization is a high rank attained by one who exerts effort and dedicates time. The Prophet, peace and blessings be upon him, said: "Take care of this Qur’an, for by the One in whose hand is Muhammad's soul, it escapes more readily than a camel from its hobbles." It was narrated from Ibn Amr that whoever recites the Qur’an has nurtured prophethood between his sides, though no revelation comes to him. A Muslim should preserve what he has memorized, dedicate time for revision and further memorization, and abandon sins and disobedience, which cause forgetfulness of the Qur’an.