Musnad Ahmad 2:4

'Affan narrated to us, 'Abd al-Wahid ibn Ziyad narrated to us, he said: 'Asim ibn Kulayb narrated to us, he said: My father said: I narrated it to Ibn 'Abbas. He said: "And what is it that amazes you about that? When 'Umar, may Allah be pleased with him, would invite the elders from the companions of Muhammad, may Allah bless him and grant him peace, he would invite me along with them. He would say: 'Do not speak until they speak.'" He said: So he invited us one day, or one night, and said: "Indeed, the Messenger of Allah, may Allah bless him and grant him peace, said regarding the Night of Decree what you have already known. So seek it in the last ten [nights] on the odd [numbered] ones. So in which of the odd [nights] do you see it?"