Renting out part of the mosque in order to make money from it
Question

                What is the ruling on leasing part of the mosque building for business and spending the income on the mosque?.
Praise be to Allah.
      If this part of the building is not needed for prayer, then 
      there is nothing wrong with renting it out for permissible purposes that 
      are appropriate to the status and sanctity of the mosque, on condition 
      that the majority of the people of the mosque agree to that. That is based 
      on the ruling that disposing of a waqf and changing its form in ways that 
      will benefit it is permissible. 

    The Hanbalis regard it as permissible to raise the mosque and 
    build shops beneath it for a purpose. Renting out part of the mosque to 
    cover its expenses comes under the same heading. 

    In Kashshaaf al-Qinaa‘ (4/375) it says: It is 
    permissible to raise the mosque if most of the people in the location -- 
    i.e., its neighbours -- want that, i.e., raising it and putting shops 
    underneath it which will benefit people. Imam Ahmad stated that according to 
    a report of Abu Dawood, because of the benefits it brings. And the apparent 
    meaning is that it is permissible because of the benefits it brings and the 
    interests it serves. End quote. 

    See: Majmoo‘ al-Fataawa by Shaykh al-Islam Ibn 
    Taymiyah (31/219); Fataawa al-Shaykh Muhammad ibn Ibraaheem (9/207). 

    And Allah knows best.