It was narrated that Ibn 'Umar said:
"When 'Umar bin Khattab was appointed caliph, he addressed the people and said: 'The Messenger of Allah permitted temporary marriage for us three times, then he forbade it. By Allah, If I hear of any married person entering a temporary marriage, I will stone him to death, unless he can bring me four witnesses who will testify that the Messenger of Allah, allowed it after he forbade it'."
English reference: Vol. 3, Book 9, Hadith 1963
Arabic reference: Book 9, Hadith 2039