The Articles of Faith, Part 2
Section 5 of 31 · Foundations of Islam · Hamza Yusuf
Four Witnesses
Here is an example. In Islamic law, if a man finds his wife in bed with another man, can he kill her? Absolutely not. He has to have four witnesses who see penetration. That is pretty impossible — and one would have to be pretty perverse to go into a room and try to see that, if people are under covers. You cannot do it. Not just being on top of one another: seriously, it is penetration that must be witnessed.
The only recourse he has, if he does find that, is that immediately he has to do what is called mulāʿanah. He goes to a qāḍī and says: I found my wife in bed. Then the wife is brought, and they do this mulāʿanah, which is a mutual cursing: each one swears that the other is lying, and on the fifth time they call the curse of Allah upon themselves. If she does that, then she is absolved. But there is a permanent divorce, and the child does not go to his lineage: the child is not considered his child. If she does not, then she would be guilty of adultery.
Why is it set up this way? Because it is related to lineage. That is the only reason. It is related to lineage. Islam is a patrilineal teaching.