Abu al-Khayr (may Allah have mercy on him) said: I saw Abu Tamim al-Jayshani pray two rak'ahs before the prayer when he heard the adhan of Maghrib. I came wanting to stop him, whereupon Sayyiduna Uqbah bin Amir (may Allah be pleased with him) said: "We used to do this in the time of the Messenger of Allah (peace and blessings be upon him)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14865