What does Islam say about 'Zina' Fornication and Adultery?

Allah the Most High says in the Qur’an: "And come not near to unlawful sex, it is a transgression, a great sin, and an evil way." (Surah Al-Isra’, 17:32)

Allah says: "Verily, those who like that (the crime of) illegal sexual intercourse should be propagated among those who believe, they will have a painful torment in this world and in the Hereafter. And Allah knows and you know not.” (Surah An-Nur, 24:19)

One of the companions of the Prophet (Peace be upon him) narrated:

'Some pagans, who committed murders in great number and committed illegal sexual intercourse excessively, came to Muhammad and said: "O Muhammad! Whatever you say, and invite people to is good, but we wish if you could inform us whether we can make an expiation for our (past evil) deeds." So the Divine Verses were revealed:

"Those who invoke none along with Allah, nor kill such person as Allah has forbidden, except for a just cause, nor commit illegal sexual intercourse-and whoever does this shall receive the punishment.” (Surah Al-Furqan, 25:68)

In Islam 'Zina' (fornication/adultery) is considered a major crime and great sin.

Is there a punishment for this in Islam?

Allah says in the Qur’an: "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 (illegal sex), the punishment is to stone them to death, according to Allah's Law).” (Surah An-Nur, 24:2)

Allah's Messenger (Peace be upon him) judged that the unmarried person who was guilty of illegal sexual intercourse be exiled for one year and receive the legal punishment (i.e. be flogged with one hundred stripes). (Reported by Sahih al Bukhari #6833)

A man from Bani Aslam came to Allah's Messenger (Peace be upon him) and informed him that he had committed illegal sexual intercourse and he bore witness four times against himself. Allah's Messenger (Peace be upon him) ordered him to be stoned to death as he was a married person. (Reported by Sahih al Bukhari #681)

Did other religions practice this punishment?

The book of Deuteronomy 22:20-25 clearly states: "If, however, the charge is true and no proof of the girl's virginity can be found, she shall be brought to the door of her father's house and there the men of her town shall stone her to death. She has done a disgraceful thing in Israel by being promiscuous while still in her father's house. You must purge the evil from among you. If a man is found sleeping with another man's wife, both the man who slept with her and the woman must die. You must purge the evil from Israel If a man happens to meet in a town a virgin pledged to be married and he sleeps with her, you shall take both of them to the gate of that town and stone them to death - the girl because she was in a town and did not scream for help, and the man because he violated another man's wife. You must purge the evil from among you. But if out in the country a man happens to meet a girl pledged to be married and rapes her, only the man who has done this shall die."

One of the companions of the Prophet narrated that a Jewish man and a Jewish woman who had committed Zina (fornication) were brought to the Messenger of Allah. The Messenger of Allah (Peace be upon him) went to the Jews and said: "What do you find in the Torah about the one who commits Zina?" They said: "We make them sit backwards (on mounts) and parade them around." He said: "Bring me the 'Torah' if you are telling the truth." They brought it and read it, and when they reached the Verse of stoning, the person who was reading placed his hand over the Verse of stoning and read that which came before it and that which came after it. One of the companions who was with the Messenger of Allah (Peace be upon him) said to him: "Tell him to lift his hand," so he lifted it, and there beneath it was the Verse of stoning. So the Messenger of Allah ordered that they be stoned."(Reported by Sahih Muslim, Book of Oaths Hudud #26)

This practice was even mentioned in the Torah and has been practiced by many Jews throughout history. Therefore, Islam re-enforced this divine commandment and didn't invent this punishment. Once again, Allah from His All-Encompassing Wisdom and Knowledge knows what's best for His creation and only legislates that which protects His creation from harm. Furthermore, when this punishment is carried out upon this person, it serves as an expiation for this great sin. And Allah knows best.

Why should someone be punished like this?