What is the legal ruling on returning the one million dinars I received from the seller: should I return the same amount to him, or its current value? And if I return the current value, is it permissible for me to deduct 2,500,0 dinars—which is the amount of losses I incurred because of him—from the amount due to him, by way of "taking possession of one's right"?

The default is that litigation expenses are to be covered by the public treasury (Bayt al-Mal). If this is not possible, then the expenses are to be borne by the claimant, unless the opponent is stubborn and their injustice is clear, without any bias from the judge, in which case the expenses fall upon the defendant.

Ibn Asim said: "The fee for assistance is on the seeker of truth, and on anyone else if he is stubborn, it becomes due."

If the right is clear, the defendant is solvent, and the judge is just, then the procrastinator must bear the expenses, unless they have an excuse.

Therefore, if the seller refuses to grant the buyer's right, and the buyer is forced to sue them, and their stubbornness becomes evident, then the litigation costs will be borne by the seller in the usual manner.

In this case, the buyer is permitted to take the one million [currency unit] that is in their possession by way of rightful seizure (Dhafr), and claim the remaining usual costs. If the expenses are less than one million, they must return the surplus, without considering any change in value.