The Muslims celebrate Eid twice a year, Eid-ul-Fitr and the other, which comes about 10 weeks later, is called Eid-ul-Adha.
Eid-ul-Azha (Festival of Sacrifice) is a festival comes about ten weeks after Eid-ul-Fitr, and marks the completion of Hajj (Holy pilgrimage to Mecca). It is the festival of Sacrifice that commemorate the obedience of Hadhrat Ibrahim and his son Hadhrat Ismail to the commandment of Allah. Hadhrat Ibrahim had a series of dreams in which he saw himself sacrificing his eldest son Ismail. He inferred that it was perhaps the will of God that he should sacrifice the life of his son.
Hadhrat Ibrahim, being most obedient to God, was about to sacrifice the life of his son Ismail, when God commanded him to stop and gave him the good news that he had indeed fulfilled His command. God was so pleased with Ibrahim because of his obedience that He multiplied his progeny into billions. He was also given the great honor of being the forefather of the Holy Prophet of Islam . On the day of Eid those Muslims who can afford to sacrifice an animal are enjoined to do so after Eid Prayer.