Yahya related to me from Malik that he had heard that a man askedAbdullah ibn Umar whether the witr was obligatory and Abdullah ibnUmar said, "The Messenger of Allah, may Allah bless him and grant himpeace, prayed witr, and the muslims prayed witr." The man beganrepeating his question, and Abdullah ibn Umar kept saying, "TheMessenger of Allah, may Allah bless him and grant him peace, prayedwitr, and the muslims prayed witr."
App reference: Book 7, Hadith 17
USC-MSA web (English) reference: Book 7, Hadith 17
Arabic reference: Book 7, Hadith 271