What is the ruling on building mosques under houses, and is it permissible to pray the Friday prayer and congregational prayers in them? What is the ruling on this practice?

Question:
What is the ruling on building mosques under houses? Is it permissible to pray the Friday prayer and congregational prayers in them? What is the ruling on this practice? May Allah reward you with good.

Answer:
There is nothing wrong with that, for such mosques are pure in themselves for the worshippers, so there is nothing wrong with that, even if there are houses above them, or if they are above the houses. This is especially the case when there is a need for it, such as when the area is narrow and the buildings are crowded. There is nothing wrong with making the ground floor a mosque, or the upper floor a mosque, provided it is built and prepared for the worshippers; there is no blame in that, and praise be to Allah. However, whenever it is possible to have the mosque in a separate building with its facilities and expansions, that is better and more complete.