Is an individual's dwelling in a house built on land not owned by him—such as land belonging to the State Treasury or to several heirs—in areas like refugee camps considered unlawful and an unjust acquisition of property?

It is not permissible to encroach upon land by building, residing, or utilizing it in any other way without the permission of its owners, whether they are heirs or the state. The property of a Muslim is inviolable except with their willing consent. All of a Muslim is sacred to another Muslim: his blood, his property, and his honor. And whoever disposes of the wealth of Allah without right, for him is the Fire on the Day of Resurrection.