What is the ruling on the apartment that the mother-in-law registered to the questioner's wife, given that the questioner knows that the mother-in-law profits from zina (adultery/fornication) and he refuses to take anything from her, while his wife wants to donate a portion of this money to purify it?

The earnings of an adulteress are unlawful (haram (definition)) and impure (khabith). If all of an adulteress's wealth comes from adultery, then it is forbidden to accept her gift or inherit her money. However, if she possesses other lawful wealth, then accepting her gift is not forbidden but disliked, unless it is from the very essence of the unlawful money, in which case it is forbidden. It is preferable to reject money received from her mother.

If a woman's wealth is mixed, containing both lawful and unlawful elements, then the heir must strive to ascertain the amount of the unlawful money and give it as charity to the poor or for good causes, then take what remains. If the matter is entirely obscure, it is permissible to divide the money in half: inherit one half and give the other half in charity.