Rib'i bin Hirash narrates from one of the Companions (may Allah be pleased with him) that the people began the morning fasting on the thirtieth day. Then two Bedouins came and testified that they had seen the crescent the day before, so the Messenger of Allah (peace and blessings be upon him) commanded the people "to break their fast."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8188