What is the ruling on the sale of a plot of land by the original owner's agent to an unknown third party, and who has the right to the sale proceeds after the original owner had sold it to his sister and her husband through a suspended sale in which ownership was not transferred?

Firstly: It is permissible for the state to sell lands on the condition that they are not sold or gifted until they are built. This restriction on what is permissible is for the public interest, and it falls under the principle of valid sale and condition, as long as it does not contradict Islamic law.

Secondly: Selling the land before building on it, in violation of the state's condition, makes the seller a transgressor, but the sale itself is valid, and any profit the buyer makes from reselling it is his property.