Musnad Ahmad 1060:83

Hammad ibn Khalid narrated to us, from Ibn Abi Dhi'b, from Yazid ibn Abi Habib, from a man, from Abu Ayyub, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Perform the Maghrib prayer when the fasting person breaks his fast, and hasten before the rising of the stars."