To enforce the punishment for adultery, it must first be proven to have occurred. The proof required is either four confessions by the doer, or the testimony of four witnesses.

The mandatory punishment for adultery

An adulterer can be either a muhsan or a non-muhsan. A person is defined as muhsan if he or she meets the following conditions:  

1) Having had normal and legitimate sexual intercourse.

2) The preceding intercourse was in a legitimate marital relationship; and 

3) Both man and woman must be at the time of their sexual intercourse sane, free adults. 

Thus, a muhsan person is one who has had sexual intercourse with his wife when they both were lawfully married and free, sane adults. This makes four conditions that must be met for the mandatory punishment for adultery to be enforceable: adulthood, sanity, freedom and a previous sexual intercourse in a legitimate marriage.

The mandatory punishment for adultery is stoning to death, whether the adulterer is a man or a woman. This punishment is confirmed to have been stated and done by the Prophet (peace be upon him).

It is reported that 'Umar addressed the people as follows: 

An adulterer who does not meet the above-mentioned conditions that make a person muhsan is given a lesser punishment. The punishment in this case is 100 lashes and exile for one year. To send the woman adulterer into exile, she must be accompanied by a mahram, i.e. a relative whom she is forbidden to marry, such as her father or brother.

Ubadah ibn al-Samit reports that Allah’s messenger said:

Exile means sending the adulterer away from his home town.

Scholars differ on whether the physical punishment should be combined with a year’s exile.

 Al-Shafi'i and Ahmad ibn Hanbal confirm that both are applicable. Malik and al-Awza'i consider that the adulterer is sent into exile and punished physically, but the woman adulterer is not. Abu Hanifah maintains that exile is not added to the physical punishment unless the judge considers that it serves an important purpose. In this case he orders exile, as he determines.

Proof

Before the punishment for adultery is enforced, the crime must first be proven to have occurred. The proof required is one of two things: the first is four confessions by the adulterer, even if these confessions are made at different times. The Prophet (peace be upon him) accepted the confessions of Ma'iz and the Ghamidia woman. Four confessions are required because when Ma'iz confessed three times, the Prophet (peace be upon him) sent him away. Only when he added a fourth confession did the Prophet (peace be upon him) enforce the punishment.

When a confession is made, the person making the confession must make absolutely clear that he has had penetrative intercourse. The reason is that he may speak of adultery but means only having had some pleasure with a woman without actually going as far as penetrative intercourse. In that case, no mandatory  prescribed punishment is due. When Ma'iz made his confession before the Prophet (peace be upon him), the Prophet (peace be upon him) said to him: ‘Perhaps you might have only kissed the woman or played with her?’ Ma[iz said: “No...” The Prophet (peace be upon him) repeated his questioning, wanting to make clear that the man meant full intercourse. He hoped that Ma'iz would give reason to make the case short of confirmation. When Ma'iz made it absolutely clear, doubt was removed.

It is absolutely important that the person concerned should stick by his confession throughout. The Prophet (peace be upon him) repeatedly sought confirmation from Ma'iz, hoping that he would go back on his confession. When there was no way out and the punishment had to be enforced, people stoned Ma'iz. As the stoning was going on, Ma'iz tried to escape and people chased him. When the Prophet( peace be upon him) heard of this, he said:

The other type of proof is the testimony of four witnesses.

For their testimony to be accepted, the following conditions must apply:

1-There must be four of them together. If there are less than four, their testimony is not accepted.

2-The witnesses must be sane adults. Testimony by an insane person, or a boy who has not attained puberty, is unacceptable.

3-They must be men of integrity. Women are not acceptable as witnesses to adultery because they are too honourable to witness an act of lewdness. On the other hand, a person of suspect morality and integrity is unacceptable.

4- The witnesses must have seen the act of adultery, describing it so graphically as to leave absolutely no doubt that they mean penetrative sex, not mere foreplay or similar pleasurable action.They must have actually seen the adulterer’s penis inside the woman’s vagina. 

5-The witnesses must be Muslims; as the testimony of an unbeliever in such a case is unacceptable.

6-They must give their testimony in the same session, whether they come together or separately.

If any of these conditions does not apply, the witnesses are deemed to have made a false accusation and the punishment for that offence is enforced against them all [1].

They would be flogged 80 lashes as Allah said: