All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Mut'ah (temporary marriage) is for a man to say to a woman with whom there are no marriage impediments, "I would like to enjoy you or marry you for a stipulated period", or to fix a known period in the marriage contract. The four Imaams unanimously agreed that this is prohibited. In fact, there is no difference between this temporary marriage and a person who commits Zinaa (adultery or fornication) with a woman with a fixed fee (i.e., prostitution).
There are authentic narrations about the prohibition of this marriage. For instance, Ali said to Ibn 'Abbaas and his father: “The Prophet , forbade temporary marriage and the meat of donkeys during the battle of Khaybar.''
Imaam Al-Maaziri said, "Temporary marriage was lawful in the early period of Islam and then it was abrogated due to the authentic narrations (on the subject). Moreover, the scholars agreed in a consensus that it is forbidden. It is only a group of innovators who disagreed with this as they relied on abrogated narrations upon which they have no evidence. They supported their viewpoint with the recitation of Ibn Mas'ood ‘So for whatever you enjoy [of marriage] from them to a fixed time’, and this recitation is weak and cannot be taken as evidence to be acted upon, since the authentic recitation does not state, ‘to a fixed time.’”
Qaadhi ‘Iyaadh said, "The scholars unanimously agreed that this Mut’ah was a marriage for a fixed period without resulting in the right of inheritance; the two spouses separate without divorce after the fixed period ends. Afterward the entire Muslim nation unanimously agreed that this temporary marriage is forbidden with the exception of the Raafidhah (the extreme Shee’ah).”
Ibn 'Abbaas considered this type of marriage to be lawful initially but soon afterwards he withdrew his ruling.
Moreover, the scholars unanimously agreed that if this kind of marriage takes place, it is ruled that it is invalid.
It is not true that Shaykh Al-Qaradhaawi, may Allaah preserve him, permitted it. It is also not correct to say that 'Umar invalidated it. Rather, it is confirmed that the Prophet prohibited it as we have already discussed.
To conclude, we advise you to read the book entitled Minhaaj As-Sunnah An-Nabawiyyah authored by Ibn Taymiyyah and the book entitled Al-Khutoot Al 'Areedhah authored by Muhib Ad-Deen Al-Khateeb .
Allaah Knows best.