He was asked:

About a Christian priest beside whose house there was a plot containing a ruined, roofless church. None of the Muslims knew when it had fallen into ruin. The priest purchased the plot and built on it, incorporating the church into the construction, repairing its walls, and restoring it. He then began gathering Christians there, and they publicly displayed their religious observances. Some of the authorities summoned him, but he sought strength and support from some Bedouins and openly engaged in wrongdoing.

He answered:

He has no right to establish the church described, even if the remains of an old church stood there in the territory of Syria. The Muslims conquered the territory of Syria by force and took possession of those churches. The scholars agree that they were permitted to demolish them; they disagreed only over whether demolishing them was obligatory.

No one may assist him in establishing this, and anyone who assists him must be punished. As for the non-Muslim under Muslim protection who establishes it, according to one of the two scholarly opinions, his covenant of protection is annulled, and his life may lawfully be taken and his property seized. This is because he has violated the conditions that the Muslims imposed upon them. They also stipulated that anyone who breached those conditions would become subject to whatever is permissible in the case of those at war with the Muslims.

Allah knows best.