Are the conditions of a contract based on the intention of the one stipulating them, or on the intention of each party? And is it permissible to betray a contract with a warring disbeliever with the intention of seizing his wealth?

If the door of private intentions in contracts were opened, it would lead to nullifying the meaning of the contract and the covenant, and bringing about great corruption. This is not accepted by reason, nor by Islamic law, nor by custom. Allah Almighty has commanded the fulfillment of contracts and covenants. Allah Almighty said: "O you who have believed, fulfill [your] contracts" and "And fulfill [every] covenant. Indeed, every covenant will be questioned about." The Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." The basic principle concerning contracts and conditions is validity, and the purpose of a contract is its fulfillment.