Sunan Ibn Majah 1986

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: 'O Ash'ath, learn from me something that I heard from the Messenger of Allah" 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