Musannaf Ibn Abi Shayba 3:6283

Abu Bakr narrated to us, he said: Waki' narrated to us, from Hisham ibn 'Urwah, from his father, from 'Aishah, she said: The Messenger of Allah (may Allah bless him and grant him peace) used to say: "Seek the Night of Decree (Laylat al-Qadr) in the last ten [nights] of the month of Ramadan."