What is the ruling on praying in a mosque built on land acquired through false testimony?

If the mosque builder seized the land from its owner through false testimony, then he is a usurper, and it is not permissible for him to benefit from it. The mosque must be demolished immediately, and the land returned to its owner. Prayer in this mosque, built on usurped land, is impermissible, and there is a difference of opinion regarding the validity of prayer therein: The Hanbalis consider it invalid, while the majority of scholars consider it valid, though sinful.