To what extent is the hadith of Omar Ibn Al-Khattab sound concerning the two Mutʿahs—Hajj and marriage—that existed during the time of the Messenger and which he prohibited? And what are the reasons for the prohibition of Mutʿah marriage in the Sunni school of thought?

The prohibition of mut'at an-nisa' (temporary marriage) during the Umar's era was based on the Prophet's (peace be upon him) prohibition. As for mut'at al-hajj (Hajj by combining Umrah and Hajj), it was not a prohibitive ban but rather a choice for what was best for the people, which was performing Umrah on one journey and Hajj on another. This is indicated by his statement, "If I were to perform Hajj, I would perform mut'ah," and his command to others to perform mut'ah.