What is the ruling on closing a mosque that was built for prayer and leasing it to a Quran memorization society, when there is another mosque overflowing with worshippers nearby, knowing that the owner of the aforementioned mosque refuses to open it due to family disputes?

Building mosques is one of the best acts of devotion. It is not permissible for someone who has built a structure and designated it as a waqf (endowment) — such as a mosque — to revoke their endowment. The majority of scholars hold that an endowment is established by action accompanied by contextual evidence, such as building a mosque and allowing people to pray in it. This is the view held by Imam Ahmad and Abu Hanifa.

The Shafi'is differed, holding that an endowment is only valid through explicit verbal declaration.

If the builder of the mosque wrote on its exterior, "Al-Siddiq Mosque," this indicates that he endowed it for prayer, and he does not have the right to divert it for another purpose, especially if the other mosque is small and there is severe overcrowding.

A Muslim must know that Satan is his enemy, and he must fight him, not obey him in matters that corrupt his worldly life and his afterlife.