Allah Almighty Says in the Noble Quran (what means):
"The [Unmarried] woman or [unmarried] man found guilty of sexual intercourse— lash each one of them with a hundred lashes, and do not be taken by pity for them in the religion [i.e. law] of Allah, if you should believe in Allah and the Last Day. And let a group of the believers witness their punishment. The fornicator does not marry except a [female] fornicator or polytheist, and none marries her except a fornicator or a polytheist, and that [i.e. marriage to such persons] has been made unlawful to the believers. And those who accuse chaste women (of adultery) and then do not produce four witnesses — lash them with eighty lashes and do not accept from them testimony ever after. And those are the defiantly disobedient. Except for those who repent thereafter and reform, for indeed Allah is Forgiving and Merciful." [Quran 24: 2-5]
Islamic law (Sharee'ah) prescribes a very heavy penalty for adultery. However, Islam does not legislate such a penalty without first putting in place sufficient legislation that protects people against falling in sin. It also ensures that the punishment is not enforced except in cases where there is certainty about the offence and its perpetrators. Islam is a complete code of living that is not based on punishment. Its basis is to provide all that promotes a clean and morally pure life. If some individuals then abandon such a clean and easy life in order to deliberately submerge themselves into filth, they incur such heavy penalty.
In the case of adultery, Islam requires four witnesses to testify that they have seen the offence, or else, a clear and confirmed confession by the perpetrators.
It may be suggested, then, that the punishment is unreal and unenforceable, which renders it ineffective as a deterrent. Punishment is not the basis of the Islamic approach; its basis is prevention, education and cultivating people’s finer feelings and consciences so that they refrain from even contemplating this offence.
Imaam Maalik 
narrated that a man confessed to fornication in the time of the Messenger of Allah 
. The Messenger of Allah called for a whip, and he was brought a broken whip. He said: "Above this," and he was brought a new whip whose knots had not been cut yet. He said: "Below this," and he was brought a whip which had been used and made flexible. The Messenger of Allah gave the order and he was flogged. Then he said: "O people! Observe the limits of Allah. Whoever has committed any of these ugly things (adultery or fornication) should cover them up with the veil of Allah. Whoever reveals to us his wrong action, we shall perform what is in the Book of Allah against him (i.e. the prescribed penalty)." [Maalik]
Prescribing a very harsh punishment for adultery is not sufficient, on its own, to protect the Muslim community and ensure the purity of its atmosphere. Therefore, a supplementary order is given to isolate the adulterers from the rest of the Muslim community. It goes further to remove the air of the offence from the Muslim community, prescribing a heavy punishment for those who accuse chaste women of adultery without providing firm evidence in support of their accusation. Allah Almighty Says in the Quran (what means):
“And those who accuse chaste women of adultery and then do not produce four witnesses — lash them with eighty lashes and do not accept from them testimony ever after. And those are the defiantly disobedient. Except for those who repent thereafter and reform, for indeed Allah is Forgiving and Merciful".” [Quran 24: 2-5]
Allowing people to accuse chaste women, whether married or not, without a clear proof means that people could always make up such accusation, fearing no repercussion. This means that the Muslim community finds itself with a stained reputation. Every individual is threatened with false accusation. Every man suspects his wife, and every wife suspects her husband, and people doubt their legitimacy. In such an intolerable state of doubt and suspicion, every family is undermined. Moreover, when such accusations are frequently made, those who steer themselves away from adultery will begin to think that the crime is common in society. Thus, people begin to think about adultery in a different spirit, with its ghastly nature sounding less ghastly as a result of its frequent mention. Those who would not have contemplated it at all may begin to think of doing so, feeling that many others are doing it.
Thus, in order to protect people’s honor and their suffering from suspicion as a result of uncorroborated accusations, the Quran prescribes for false accusation a punishment that comes close to that of adultery. The punishment is flogging with 80 stripes, rejecting their testimony in any case or situation, and giving them the label of transgressors. The first part of the punishment is physical, while the second is moral. It is sufficient that the accuser is deprived of the right to testify, and considered deceitful. The third part of the punishment is a religious one. The one guilty of false accusation is following a line that deviates from that of faith. The only way to protect himself from such punishments is that the accuser should provide four witnesses who have seen the offence being committed, or three alongside him if he himself has seen it.
It is agreed upon by Muslim scholars that for adultery (or fornication) case to be authentically proven, four witnesses must simultaneously see, by their own eyes, the man's sexual organ inserted in the woman's sexual organ. Only when these four witnesses give such testimony is the accusation proved and the punishment of adultery (or fornication) is enforced on the perpetrators.
Such restrictions are set forth by Sharee'ah in order to limit to the least minimum the possibility of falsely accusing chaste women of adultery (or fornication), which leads to social and psychological troubles for the accused women. Even when such a sin –adultery (or fornication) - is committed, such restrictions laid by Sharee'ah will guarantee the suppression of the crime and prevents its spread among the people, which contaminates the morally pure Muslim community.
