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

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.