If the day of Eid is not determined until late in the day (past the time of the Eid prayer), then the Eid prayer is held the next day. Abu `Umayr Bin Anas reported that some of his uncles, who were from the Ansar, and who were companions of the Prophet (peace be upon him), told him:
"The crescent of Shawwal was obscure to us. So we continued to fast that morning; later in the day, a group of travelers arrived and testified before Allah's Messenger (peace be upon him) that they had seen the hilal (crescent) the previous day; so he (peace be upon him) commanded the people to break their fast on that day, and to go out to the musalla the following morning."