Musannaf Ibn Abi Shayba 3:5003

Ghundar narrated to us, from Shu'bah, from Ya'la ibn 'Ata, from Abu Fazara, who said: I asked Anas about the two rak'ahs before the Maghrib prayer. He said: "We used to hasten to perform them during the time of the Messenger of Allah, may Allah bless him and grant him peace."