What is the ruling regarding a married man and a married woman discussing sexual matters and desiring each other, and is it permissible for the man to marry the woman after her husband's death, and what is their punishment in Islamic law?

The aforementioned discourse is impermissible except between spouses. Its occurrence between two non-mahram individuals is a reprehensible act. The sin increases if it is with a married woman, as it constitutes a dereliction of duty towards Allah and her husband, and a betrayal of him. They must repent immediately and sever the relationship. There is no specific prescribed punishment in Islamic law for this sin, but the ruler may impose a disciplinary punishment upon the perpetrator as he deems deterrent. The man's justification for engaging in this relationship is a mockery of honor. A sensible person would not approve of such a thing for his wife, so how could he approve of it for the wives of others? In a hadith, the Prophet, peace and blessings be upon him, illustrated the ugliness of an act of zina to a young man who desired it by asking him if he would like it for his mother, daughter, sister, paternal aunt, or maternal aunt. After the young man replied in the negative, the Prophet, peace and blessings be upon him, supplicated for him, and he repented.