It was narrated that Ash' ath bin Qais said: "I was a guest (at the home) of 'Umar one night, and in the middle of the night he went and hit his wife, and I separated them. When he went to bed he said to me: '0 Ash' ath, learn from me something that I heard from the Messenger of Allah P.B.U.H: "A man should not be asked why he beats his wife, and do not go to sleep until you have prayed the Witr:" And I forgot the third thing." (Hasan) Another chain with similar wording.