Musannaf Ibn Abi Shayba 4:646

Shababa ibn Sawwar narrated to us, from Layth ibn Sa'd, from Yazid ibn Abi Habib, from Abdullah ibn Hubayb, from Abdullah ibn Unays, the companion of the Messenger of Allah, may Allah bless him and grant him peace, that he was asked about the Night of Decree (Laylat al-Qadr). He said: "I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: 'Seek it tonight,' and that night was the night of the twenty-third."