Issue: A man finds another man—may Allah protect us—committing adultery with his wife. Is his punishment a matter of repelling an assailant?
Answer: No. Rather, it falls under punishing the aggressor. If he finds him with his wife, he may take up the sword and cut him in two without warning. For this, as Shaykh al-Islam also stated, is a case of punishing the aggressor.
Such a case occurred during the caliphate of Umar ibn al-Khattab, may Allah be pleased with him. A man entered upon his wife and found another man with her. He took a sword and cut him in two. The relatives of the slain man demanded retaliation for his blood, and the parties brought their case before Umar ibn al-Khattab, may Allah be pleased with him. The man said, “By Allah, O Commander of the Believers, if anyone was between my wife’s thighs, I killed him.” Umar said, “What do you say?” They replied, “Yes.” So Umar, may Allah be pleased with him, took the sword, shook it, and said to him, “If they return, then return.” (1) This is because it is a case of punishing the aggressor; that is, we punish such an offender without warning.
His statement: “Whoever enters a man’s home stealthily”: even if he is not one of the thieves, he entered furtively, intending to take something from that house.
His statement: “His ruling is likewise”: that is, like one who assaults another’s property. He is to be repelled by the least severe means possible; if he cannot be repelled except by killing, then he is killed.
If he says, “I entered seeking a book that I wanted to consult; I did not intend to…”