What is the ruling of Islamic law on reclaiming land sold seven years ago, after the buyer refused to return it, and the local authority ruled that it be handed over to the seller due to the buyer lacking a legal title deed?

As long as you admit that you sold it to him, you have no right to take it from him except with his consent, either as a gift or through purchase. Taking it from him by force of authority is injustice and aggression. You must respect the sale and leave it in the hands of its rightful owner, unless he wishes to sell it to you or gives it to you as a gift. The Prophet, peace and blessings be upon him, said: "Beware of injustice, for injustice will be darknesses on the Day of Resurrection," and "Indeed, your blood, your properties, and your honor are sacred to one another."