How authentic is the Hadeeth narrated on the authority of ‘Umar ibn Al-Khattaab, may Allaah be pleased with him, concerning the two things that existed at the time of the Prophet, sallallaahu ‘alayhi wa sallam, that he (i.e. ‘Umar) forbade (i.e. the Tamattu‘ Hajj and Mut‘ah marriage)? What are the reasons for forbidding the Mut‘ah marriage in the Sunni methodology?

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.

It is narrated on the authority of Jaabir that he said: "We used to contract Mut‘ah marriages of only a few days for a handful of dates and flour during the time of the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, and that of Abu Bakr until ‘Umar forbade it in the case of ‘Amr ibn Hurayth." [Muslim]

An-Nawawi said: "This Hadeeth implies that those who practiced Mut‘ah marriage at the time of Abu Bakr and ‘Umar did not know about the abrogation of such a marriage."

Moreover, Al-Haafith ibn Hajar said: "It is also understood that ‘Umar did not forbid Mut‘ah marriage based on his personal reasoning. Rather, he did so based on the forbiddance of the Messenger of Allaah, sallallaahu ‘alayhi wa sallam."

Thereby, it is known that ‘Umar's forbiddance of Mut‘ah marriage, for those who did not know about it being abrogated, was not based on his personal reasoning but was in compliance with the command of the Prophet, sallallaahu ‘alayhi wa sallam.

As for Tamattu‘ Hajj, it is authentically attributed to ‘Umar that he forbade it but such forbiddance did not entail it being unlawful. Rather, it was meant to choose for the people what is better for them which is to perform ‘Umrah and Hajj, each with a separate journey. ‘Umar believed that this was what is implied by the Command of Allaah The Almighty as He Said (what means): {And complete the Hajj and ‘Umrah for Allaah}[Quran 2:196] 

This is so even though it is authentically attributed to ‘Umar that he said: "If I would perform Hajj, I would perform a Tamattu‘ Hajj and if I would perform Hajj once again, I would perform a Tamattu‘ Hajj." [Al-Athram] ‘Umar was also reported to have said, "If you intend both Hajj and ‘Umrah with your Ihraam, you are guided to the Sunnah of your Prophet, sallallaahu ‘alayhi wa sallam." [An-Nasaa’i]

This is also supported by the fact that Ibn ‘Umar used to order the people to perform Tamattu‘ Hajj and, when they said to him that his father forbade it, he would reply saying: "He did not mean that which you understood."