What is the ruling on selling an old and small mosque to Muslims when it is expected that Christians will buy it from them and convert it into a church, and is this considered aiding them in polytheism and misguidance?

Scholars have differed on the ruling concerning selling a mosque. The Hanbalis are of the view that it is permissible to sell a mosque that is disused or abandoned, and its price should be spent on another mosque, and this is the soundest opinion. Meanwhile, the majority (Hanafis, Malikis, and Shafi’is) are of the view that selling an endowment is absolutely impermissible.

If it is permissible to sell an old, disused mosque, it is not permissible to sell it to someone who will use it as a church or a place for committing sins, based on the jurisprudential rule: “Means take the ruling of their ends.” Thus, a Muslim selling land or a house to be taken as a church is forbidden by Islamic law.

It is forbidden to sell a mosque to disbelievers if it is known or highly probable that it will be converted into a church or other houses of disbelief. However, if the buyer's intention is unknown and his state is not ascertained, then selling to him is permissible.

Advice: It is not permissible to sell a mosque unless its benefits have ceased. It is preferable to keep it as an endowment and convert it into a library or a charitable institution.