What is the ruling on one who opposes the building of a mosque on vacant land out of covetousness for the site, thereby depriving the residents of the neighborhood from praying therein, and what should the residents of the neighborhood do regarding this person?

As long as the person does not own the plot of land, he has no right to prevent the construction of a mosque on it if it benefits the residents of the neighborhood. He should be advised that the interest of the community takes precedence, and the matter should be referred to the responsible authorities to decide on building the mosque if they deem it beneficial.