Musannaf Ibn Abi Shayba 3:4899

Waki’ narrated to us, from ‘Abd al-Wahid ibn Ayman, from his father, from Tubay’, from Ka’b ibn Mati’: He said: Whoever prays four [rak’ahs] after the ‘Isha’ [prayer], perfecting the bowing and prostration in them, they are equivalent to the like of them from the Night of Decree (Laylat al-Qadr).