The celebration of Eid-al-Ahda is to commemorate the Prophet Ibrahim’s devotion to Allah and his readiness to sacrifice his son, Ismail. Allah later on replaced Ismail with a ram, which was the sacrifice in replace of his son. The command from Allah was a test to see prophet Ibrahim’s willingness and commitment to obey the lord's command, without question. That is why Eid-al-Adha means the festival of sacrifice.
Eid-al-Ahda is on the tenth day in the final (twelfth) month of the Islamic Lunar Calendar: Dhu-al-Hijjah. The day the celebrations falls on is dependent on a legitimate sighting of the moon, following the completion of the annual Holy pilgrimage of Hajj- which is an obligation for all Muslim’s who fit specifi criteria, one of the Five Pillars of Islam.