What is the ruling on developing surplus funds from the proceeds of an endowment (waqf) designated for the descendants of the endower, engaging in trade with it, and taking a percentage for its development, given that the reason for the surplus is the beneficiaries' current lack of need for the proceeds?

The revenue of a waqf (endowment) must be spent on its beneficiaries. Its administrator is not permitted to invest it except with the permission of the beneficiaries. If there are no beneficiaries for the revenue, or if there are beneficiaries but there remains an surplus beyond their needs, then the excess should be spent on charitable causes.