my husband committed zina.
Just to correct you it is not 3 witnesses but it is 4 witnesses and the condition is that they all have to have seen the male and female on top of each other having sexual intercourse.
If one of them is married he or she are stoned to death, and the other gets lashes and if they are both married then they get stoned to death but if they are not married then they only receive lashes just like Allah says, [The Zaniyah and the Zani, flog each of them with a hundred stripes] [24 v2]
If there are 4 witnesses who saw it happened or they confess then the stoning is implemented, but if the wife sees the husband or the husband sees the wife having sexual intercourse with someone else then in this case they both have the Oath one saying he saw it and the other saying it didn't happened then they are both to be released and left alone nothing happens in this case except that Allah curse is upon the liar. just like Allah says, [And for those who accuse their wives, but have no witnesses except themselves, let the testimony of one of them be four testimonies by Allah that he is one of those who speak the truth. And the fifth (testimony); invoking of the curse of Allah on him if he be of those who tell a lie. But she shall avert the punishment from her, if she bears witness four times by Allah, that he is telling a lie. And the fifth; should be that the wrath of Allah be upon her if he speaks the truth] [24 v6,7,8,9]
And also if one accuses an Innocent person without a prove and he or she is not marry to the accuser then their punishment is as Allah says, [And those who accuse chaste women, and produce not four witnesses, flog them with eighty stripes, and reject their testimony forever. They indeed are the rebellious] [24 v4]