Hadith No: 2
Ahmad ibn Hanbal - Musnad al-Imam Ahmad ibn Hanbal - Musnad of the Ten Promised Paradise
Musnad of the Rightly Guided Caliphs - The Beginning of the Musnad of Umar ibn al-Khattab (ra)
Volume: (1) - Page Number: (50)
353 - Abu Abdullah Muhammad ibn Ja'far narrated to us, who said: Shu'bah narrated to us, from al-Hakam, from 'Imarah ibn 'Umayr, from Ibrahim ibn Abi Musa,
from Abu Musa that he used to issue fatwas permitting temporary marriage (mut'ah). Then a man said to him: "Hold on a moment with some of your fatwas, for you do not know what the Commander of the Faithful has instituted in the rites after you." He met him later and asked him. Umar (ra) said: "I knew that the Prophet (peace be upon him and his holy progeny) had done it with his companions, but I disliked them to remain in that state,
married in the thickets, and then go out for Hajj with their heads dripping."