Please refer to the link of chapter 6 in the following link. The scholars have enlightened on it in the light of Quran and various hadith’s in Sahih books.
http://www.al-islam.org/encyclopedia/
BTW, similar to nikkah a siga is also recited for Mutah.
Taboo, i wouldn’t nauzubillah compare prosititution with Mutah. Unlike Prosititution, the woman is well protected and any kids born from Mutah get inheritance from dad and so on. Mutah is quite similar to a normal marriage. Like the nikkah the guy and girl have to recite a siggah for the marriage. If a concept of temporary marriage is not acceptable in islam, why would the clause of divorce be allowed in islam to begin with? A guy and girl can marry each other share a halal relationship and than have a divorce.. divorce is acceptable in islam isnt it.
Now why is mutah allowed in islam, I would believe Allah knows the best, It was a practice introduced during the time of Prophet and was practiced during his lifetime.
Allah knows human… our bodies contiously produces harmones which controls our derive… wat if one cannnot find a mate or could not marry for some xyz reason. Allah knows the best .. it would prevent him from a sin. We cannot label a practiced allowed by Allah as nauzubillah prostitution.. Allah knows the best.. There are so many other things we do beacause they are halal and precribled in the religon. People making rounds of Kaba, or kissing hajjre aswad.. do you label any of the other deeds prescribed or allowed by Allah SWT?
Quran testified islam was perfect and complete at the time of Prophet P.B.U.H.
“Today I have perfected your religion and completed my favour upon you, and I was satisfied that Islam be your religion.” (Qur’an 5:3)
What right does Hazrat Umar has to rule out a practice halal during the time of Prophet Mohammad P.B.U.H.