Musannaf Ibn Abi Shayba 3:4896

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from Husayn, from Mujahid, from Abdullah ibn Amr, who said: Whoever prays four [rak'ahs] after the 'Isha [prayer], they are like their equivalent from the Night of Decree (Laylat al-Qadr).