The Verse of Mut'ah[1] was revealed in Allah's Book, so we performed it with Allah's Apostle, and nothing was revealed in Qur'an to make it illegal, nor did the Prophet prohibit it till he died. But the man (who regarded it illegal) just expressed what his own mind suggested.

'Imran b. Husain sent for me during his illness of which he died, and said: I am narrating to you some ahadith which may benefit you after me. If I live you conceal (the fact that these have been transmitted by me), and if I die, then you narrate them if you like (and these are): I am blessed, and bear in mind that the Messenger of Allah combined Hajj and Umra. Then no verse was revealed in regard to it in the Book of Allah (which abrogated it) and the Apostle of Allah did not forbid (from doing it). And whatever a person (Umar) said was out of his personal opinion.