Is it permissible to build a masjid on the land of a derelict cemetery, especially when it is not known…

Answer

There is no objection to doing so provided that the land of the cemetery is not: [a] an endowment, [b] private property, [c] a facility for the public at large, or [d] a piece of land for holding ceremonies and building the masjid does not entail desecrating the graves or exhuming the bodies of Muslims.