Musannaf Ibn Abi Shayba 3:4277

Waki’ narrated to us, from Sufyan, from Abu al-Sawda’ al-Nahdi, who said: I prayed Maghrib, then I prayed it again in congregation. When the Imam said the taslim, I stood up and performed one rak'ah to make it even (shaf'). I asked 'Ata' about it, and he said: "You have acted intelligently."