Is a man's intimacy with his wife considered Zina (unlawful sexual intercourse)—for which he will be punished in the Hereafter—if he believed it to be permissible, but then it became clear to him that the marriage was invalid (due to a triple divorce, or apostasy and remarriage, or a suspended divorce)? And is there a difference between Zina and Sifah?

If a person faces a difficult situation that requires a legal ruling (hukm shar'i), it is obligatory for him to ask the people of knowledge. This is especially emphasized in major issues, such as matters of marriage. Whoever proceeds with a matter based on his desires without asking the people of knowledge is sinful for his negligence in clarifying the legal ruling.

However, a legal ruling (hukm shar'i) is not established as binding upon a mukallaf (accountable person) until he is aware of it. Therefore, if a man has intercourse with his wife believing it to be permissible for him, while in reality she is not permissible for him – for example, he had divorced her and forgotten, or he did not believe that the separation had occurred, or he had conditioned her divorce on something and she did it without his knowledge – then the intercourse at that time is not forbidden for him, nor is it considered adultery. The most that can be said is that he incurs sin for his negligence in clarifying the legal ruling.

Ibn Taymiyyah says: "The most apparent view is that nothing of that needs to be made up, and the address [of obligation] is not established until after communication [of the ruling]; based on His (Allah's) saying: {that I may warn you thereby and whoever it reaches.} [Quran 6:19] And His saying: {And We would not punish until We send a messenger.} [Quran 17:15] And His saying: {Lest people should have a conclusive argument against Allah after the messengers.} [Quran 4:165] And similar to this is abundant in the Quran. He (Allah) clarifies that He does not punish anyone until what the Messenger brought reaches him."