What is the ruling on saying "Indeed we belong to Allah, and indeed to Him we will return" (Istirja') and "O Allah, reward me in my calamity and compensate me with something better than it" for religious calamities, such as forgetting a part of the Qur'an or neglecting a part of the Sunnah?

Reciting "Istirja'" (إنا لله وإنا إليه راجعون - "Indeed we belong to Allah, and indeed to Him we will return") upon affliction is a Sunnah, and it is among the acts of worship through which a servant draws closer to his Lord. Allah has promised those who are patient and say, "Indeed we belong to Allah, and indeed to Him we will return," blessings, mercy, and guidance. The Prophet, peace and blessings be upon him, promised that whoever says this and adds, "O Allah, reward me in my affliction and compensate me with something better than it," Allah will reward him and compensate him with something better. The greatest affliction is a tribulation in one's religion, and among the supplications of the Prophet, peace and blessings be upon him, was: "O Allah, do not make our affliction in our religion." Forgetting the Qur'an is a great affliction, and it has been mentioned that one does not forget the Qur'an except due to a sin; thus, forgetting it is among the greatest afflictions. Neglecting the Sunnah is also an affliction. Therefore, if a Muslim is afflicted by forgetting the Qur'an or neglecting the Sunnah, he should recite "Istirja'" and ask Allah to remind him and teach him, and to help him adhere to the Sunnah, and he should strive to regain what he has lost.