The Muslim feast of Eid Al-Adha will begin on Thursday 24 September, one day later than expected as the new moon wasn't visible to Saudi Arabia's official moon-sighting body, Al-Arabiya website reported on Sunday.
Egypt's astronomical and geophysics institute previously announced that Eid Al-Adha, the second of two religious holidays celebrated by Muslims worldwide each year, would be on Wednesday 23 September.
Although Egypt has not issued a statement yet, it is likely that the country will switch its calendar, mirroring Saudi Arabia's, due to the Hajj season.
The Day of Arafah, which marks the second day of the Islamic pilgrimage rituals at the holy site of Mecca in Saudi Arabia, precedes the start of Eid Al-Adha by 24 hours, according to the Islamic calendar.
Muslims have a lunar-calendar, which is based on observing the new moon. However, moon-observation can sometimes be difficult due to clouds that limit visibility.
Eid Al-Adha lasts for four days.