(This is) a Surah (chapter of the Qur’an) which We have sent down and which We have enjoined, (ordained its legal laws) and in it We have revealed manifest Ayat (proofs, evidences, verses, lessons, signs, revelations lawful and unlawful things, and set boundries of Islamic Religion), that you may remember.
The woman and the man guilty of illegal sexual intercourse, flog each of them with a hundred stripes. Let not pity withhold you in their case, in a punishment prescribed by Allah, if you believe in Allah and the Last Day. And let a party of the believers witness their punishment. (This punishment is for unmarried persons guilty of the above crime but if married persons commit it, the punishment is to stone them to death, according to Allah’s Law).
The adulterer marries not but an adulteress or a Mushrikah and the adulteress none marries her except an adulterer or a Muskrik [and that means that the man who agrees to marry (have a sexual relation with) a Mushrikah (female polytheist, pagan or idolatress) or a prostitute, then surely he is either an adulterer, or a Mushrik (polytheist, pagan or idolater, etc.) And the woman who agrees to marry (have a sexual relation with) a Mushrik (polytheist, pagan or idolater) or an adulterer, then she is either a prostitute or a Mushrikah (female polytheist, pagan, or idolatress, etc.)]. Such a thing is forbidden to the believers (of Islamic Monotheism).
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 Fasiqun (liars, rebellious, disobedient to Allah).
Except those who repent thereafter and do righteous deeds, (for such) verily, Allah is Oft-Forgiving, Most Merciful.
And for those who accuse their wives, but have no witnesses except themselves, let the testimony of one of them be four testimonies (i.e. testifies four times) by Allah that he is one of those who speak the truth.
And the fifth (testimony) (should be) the invoking of the Curse of Allah on him if he be of those who tell a lie (against her).
But it shall avert the punishment (of stoning to death) from her, if she bears witness four times by Allah, that he (her husband) is telling a lie.
And the fifth (testimony) should be that the Wrath of Allah be upon her if he (her husband) speaks the truth
Qur’aan, Chapter 24 (Al-Noor), Verses 1 to 9