Abu Umayr bin Anas narrates from his paternal uncles, who were Companions of the Messenger of Allah (peace and blessings be upon him) (may Allah be pleased with them), that a caravan came to him (peace and blessings be upon him) and testified to sighting the crescent, saying that they had seen it the day before. So he (peace and blessings be upon him) "commanded them to break their fast and to go out to the Eid prayer-ground the next day." Shu'bah said: This was at the end of the day.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8198