Musannaf Ibn Abi Shayba 3:3557

Waki’ narrated to us, from Isra’il, from Abu Ishaq, from ‘Asim ibn Damrah, who said: I prayed Maghrib beside al-Husayn ibn ‘Ali, then I prayed two rak’ahs after Maghrib. Then I stood up to pray, and he rebuked me and said: "They are only two rak’ahs."