Does an agreement to waive a plot of land for building purposes and not for trading constitute a contract, and is the waiving party entitled to claim half of the profit when the land is sold after it has been converted for commercial purposes, and the other party has not adhered to the original agreement?

If the state grants land to its citizens without conditions, and you unconditionally relinquished your right to it to your brother, then you are not permitted to retract your gift, based on the Prophet Muhammad's (peace be upon him) saying: "He who retracts his gift is like a dog that returns to its vomit." As long as your brother owns the land, he has the right to dispose of it as he wishes, and you do not have the right to claim half its price.

However, if the state grants land under specific conditions (such as poverty, for instance) and does not permit its disposal through sale or gift, then your relinquishment to your brother is invalid, and the matter must be referred back to the state.

Your brother should treat you kindly, just as you treated him, and help you repay your debts. We advise attempting reconciliation between you two through the mediation of family and friends to preserve your brotherhood.