There is no concept of temporary marriage in Islam.It has been mentioned in many hadiths of Rasool salal laho aliehi wasalam.
Some of them are as follows:
"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. (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.' (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)." (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. (Sunan Abu-Dawud, Marriage (Kitab Al-Nikah), Book 11, Number 2068)"
From all the above mentioned hadiths it is clear that temporary marriages were declared haram by Rasool salal laho aliehi wasalam.And although they were initially halal but this cannot be an evidence for their permission because when prophet salal laho aliehi wasalam had declared it haram and cancelled its previous permission how can it be legal now.?