Is it permissible for the husband to consider the money he spent on furnishing half of the apartment registered in his wife's name as part of the expenditure for the iddah (waiting period), mut'ah (compensatory gift), and deferred mahr (dowry), especially since the amount spent might be greater than the total of these expenses, and is he religiously permitted to reclaim this money in this manner?

The money you spent on finishing half of your wife's apartment:

1. If you intended to claim it or participate in ownership: You have the right to claim it now. An agreement can be reached to deduct what is due from you, such as deferred dower, maintenance during the waiting period (iddah (definition)), and compensatory gift (mut'ah). 2. If it was a donation (gift): The general rule is that it is forbidden to revoke a gift, based on the Prophet's (peace and blessings be upon him) saying: «It is not permissible for a man to give a gift or a donation and then revoke it, except for a father in what he gives to his child...»

Exception: If you gifted her something for a specific purpose, such as improving conjugal relations, and she did not fulfill it, then it is permissible to revoke the gift. This is based on the saying of Umar ibn al-Khattab (may Allah be pleased with him): "And whoever gives a gift expecting a reward for it, then he is entitled to revoke his gift if he is not pleased with it." The meaning of "expecting a reward" is that he intended a compensation for his gift. If he did not receive that, then he is permitted to revoke it.

Anyone who receives a gift or a present due to a specific reason, its validity is tied to that reason, and it ceases to be valid when that reason ceases.

The primary justification for reclaiming it is if you did so with the intention of participating in ownership.

When reclaiming, calculate what is due to you and what is due from you, and deduct what you owe from what is owed to you.