Musannaf Ibn Abi Shayba 3:2156

'Abd al-Salam ibn Harb narrated to us, from Yazid ibn 'Abd al-Rahman al-Dalani, from 'Abd al-Malik ibn Maysarah, from Zayd ibn Wahb, that 'Umar ibn al-Khattab saw a man praying two rak'ahs after the setting of the sun and before the prayer (Maghrib), and he began to turn around. So he struck him with the whip when he finished the prayer and said, "Do not turn around, and do not make the two rak'ahs tiresome."