Question: We have a cistern from which the townspeople draw water and perform ablution, and it has a waqf whose yields exceed the cistern’s needs. We also have a needy mosque requiring repair. Is it permissible to disburse the surplus to this mosque given the cistern’s independence of need?
Answer—and Allah is the One who grants success: That is permissible given the cistern’s independence of need—namely, from what exceeds its needs and the needs of its other yields; whatever exceeds that may be disbursed to the mosque. Imām al-Mahdī Muḥammad b. al-Qāsim al-Ḥusaynī al-Hūthī—may Allah have mercy on him—issued a similar fatwa, saying this is the school’s position.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2