Abu Mas'ud (may Allah be pleased with him) says that on the morning of the thirtieth the people were fasting. Then two men 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 / 8190