Is it permissible to build a mosque on the remaining part of land endowed for a Shafi'i religious school?

The fundamental principle for managing an endowment (waqf) is to adhere to the conditions set by the endower (waqif) or to the discretion of whoever the endower authorized to oversee it. Therefore, if the endower specifically allocated the land for a school only, and there is no need for another mosque, then his condition must be observed. However, if the school does not have its own mosque, then building a mosque is considered a necessity for the school. If the endower did not restrict the land solely for the school, but rather said: "A school shall be built upon it," without other conditions, or left the matter to the supervisor, then it is permissible to build a mosque on the remaining land not needed by the school, as this fulfills a benefit consistent with the endower's purpose.