Testimony about the crescent of Eid al-Fitr reached Umar bin Abd al-Aziz (may Allah have mercy on him) at the end of the day, so he ordered the people to break their fast and said: Go out for the Eid the next day.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6284