Praying on usurped land
A plot of land, owned by the city council and designated for public benefit, was usurped by some residents who erected a mosque on it during the holidays. The city council issued a decision to remove the building because this construction violated the implemented regulations concerning the designation of land for mosques according to the zoning plan of city. Please note that four other mosques surround it, the furthest being 300m away. Is it permissible to pray in this mosque?
Scholars are unanimous on the prohibition of usurpation. Al-Nawawi said in Al-Mujmu' Sharh Al-Madhhab that there is a consensus on the prohibition of praying on usurped land. [However], scholars have two opinions on the validity of prayers performed on usurped land.
If the case is as mentioned in the question and it is ascertained that the residents have indeed encroached upon the above mentioned piece of land and violated the city council regulations concerning the building of mosques, then their action is considered usurpation. It is therefore obligatory to remove the building in accordance with the order issued by the city council.
It is unlawful to pray in this mosque.
Allah the Almighty knows best.