Is it permissible to spend Zakat funds on building an uncompleted mosque, and is it permissible to allocate a portion of the mosque's building donations to construct an attached residence for the preacher?

It is not permissible to spend Zakat funds on building mosques because Zakat has specific, divinely ordained disbursements, and building mosques is not among them. As for funds donated to the mosque, the general rule is that they should not be spent on anything other than what they were designated for, based on the statement of Ibn Hajar Al-Haytami: "The intention of the endower must be observed." However, some scholars, such as Sheikh Al-Islam Ibn Taymiyyah, held the view that it is permissible to spend endowment funds on what serves a greater benefit, even if it contradicts the endower's condition. Thus, if there is surplus money after building the mosque, it is permissible to spend it on its annexes, such as the Imam's residence, if that is for the benefit of the mosque. This is the more preponderant view as it aligns with the endower's intention of seeking reward.