Temporary Marriage (Muta) was ok, but then was later forbidden by our Prophet Muhammad peace be upon him:
In this short article we will see how and why Temporary Marriage was first allowed in Islam, but then later was forbidden by our Prophet peace be upon him:
"Rabi' b. Sabra reported that his father went on an expedition with Allah's Messenger (may peace be upon him) during the Victory of Mecca, and we stayed there for fifteen days (i. e. for thirteen full days and a day and a night), and Allah's Messenger (may peace be upon him) permitted us to contract temporary marriage with women. So I and another person of my tribe went out, and I was more handsome than he, whereas he was almost ugly. Each one of us had a cloaks, My cloak was worn out, whereas the cloak of my cousin was quite new. As we reached the lower or the upper side of Mecca, we came across a young woman like a young smart long-necked she-camel. We said: Is it possible that one of us may contract temporary marriage with you? She said: What will you give me as a dower? Each one of us spread his cloak. She began to cast a glance on both the persons. My companion also looked at her when she was casting a glance at her side and he said: This cloak of his is worn out, whereas my cloak is quite new. She, however, said twice or thrice: There is no harm in (accepting) this cloak (the old one). So I contracted temporary marriage with her, and I did not come out (of this) until Allah's Messenger (may peace be upon him) declared it forbidden. (Translation of Sahih Muslim, Book 8, Number 3253)"
Narrated 'Ali: "I said to Ibn 'Abbas, 'During the battle of Khaibar the Prophet forbade (Nikah) Al-Mut'a [Temporary Marriage in English] and the eating of donkey's meat.' (Translation of Sahih Bukhari, Wedlock, Marriage (Nikaah), Volume 7, Book 62, Number 50)"
Narrated Jabir bin 'Abdullah and Salama bin Al-Akwa': "While we were in an army, Allah's Apostle came to us and said, "You have been allowed to do the Mut'a (marriage), so do it." Salama bin Al-Akwa' said: Allah's Apostle's said, "If a man and a woman agree (to marry temporarily), their marriage should last for three nights, and if they like to continue, they can do so; and if they want to separate, they can do so." I do not know whether that was only for us or for all the people in general. Abu Abdullah (Al-Bukhari) said: 'Ali made it clear that the Prophet said, "The Mut'a marriage has been cancelled (made unlawful)." (Translation of Sahih Bukhari, Wedlock, Marriage (Nikaah), Volume 7, Book 62, Number 52)"
Narrated Saburah ibn Ma'bad al-Juhani: "The Apostle of Allah (peace_be_upon_him) prohibited temporary marriage with women. (Translation of Sunan Abu-Dawud, Marriage (Kitab Al-Nikah), Book 11, Number 2068)"
The reason why temporary marriage was allowed is to prevent illegal sex, prostitution and rape especially during the early times of Islam when Muslims didn't have residence stability and were facing all kinds of difficulties from the Pagans. The Muslim men used to also travel for long months away from their families to meet the enemy in the battle field. Some of the towns they used to go to had Muslim women in them, and like I said, to prevent adultery and fornication with any woman (Muslim or non-Muslim), and to prevent rape, the Prophet peace be upon him allowed temporary marriage contracts between Muslim men and women.
When the Muslim state became stable during our Prophet's time, he then forbidden that act because Muslims then could get married and have stable lives with their families and raise Children in a stable and convenient community.
Further explanation as to why Muta was allowed. It could probably be allowed today for some people:
Narrated Abu Jamra: "I heard Ibn Abbas (giving a verdict) when he was asked about the Mut'a with the women, and he permitted it (Nikah-al-Mut'a [Having Temporary Marriage in English]). On that a freed slave of his said to him, "That is only when it is very badly needed and women are scarce." On that, Ibn 'Abbas said, "Yes." (Translation of Sahih Bukhari, Wedlock, Marriage (Nikaah), Volume 7, Book 62, Number 51)"
I personally think that according to all of the narrations above, if the Muslim is living in a Muslim country, then he/she must not be allowed to practice Muta. But if he/she is living in a non-Muslim country and there are very few Muslims available, and marriage is not possible for one reason or another (this condition must exist), then it should not be a sin if he/she practice Muta with other Muslims, because "it is very badly needed and (men and) women are scarce" as mentioned in the above narration and verdict.
Muta is a Marriage. A man can marry up to four wives in Islam, and the woman can only marry one husband. There is a dowry for the man to pay and if children are produced in this Marriage, then it automatically becomes a permanent one. So Muta is far away from being called "legalized prostitution".
Can a Muslim couple go on a date and have Muta, as Westerners do with their illegal sex without marriage?
Absolutely not! As we clearly saw above, Muta was allowed for very special cases, and it was prohibited to be practiced by the ordinary people. Muta is not a legalization of illegal sex or prostitution. It is important for a person to know this fact very well!
Muta must not exist in Muslim countries what so ever, because there are plenty of Muslim males and females for marriage. As we clearly saw above, Prophet Muhammad peace be upon him prohibited Muta for ordinary Muslims.
Muta should only be allowed when "it is very badly needed and (men and) women are scarce" as the quote clearly says above. Even in foreign non-Muslim lands, Muslims must be extremely careful with practicing Muta. If a person knows well that he/she have the financial and physical ability to get married, and there are Muslims whom he/she can marry from, then Muta is definitely a sinful act for them, and it would be without a doubt be considered as an adultery or fornication.
If on the other hand, there are very few Muslims, and the sexual intimidation is very high for males and females as it is in the Western countries with their tight and short clothings, to bikinis in beaches, to sometimes having nude and topless beaches, etc...., and the Muslim knows well that he/she can't get married for financial and other VALID reasons, and Muta was available for them, then in my opinion, Muta marriage is allowed in that special case.
It is very difficult to put a set standard on when Muta can and can't be practiced. It really all depends on the personal situation of the Muslim. The Muslim, however needs to be very responsible and very honest toward Allah Almighty. A person can fool others with his/her lies to convince people, but they certainly can not fool their Almighty Creator.
And Allah Almighty knows best about our intentions and deeds.