Basics of Religious Education, 2nd Canadian Edition, page 147

Eid-ul-Adhiya (Eid of Sacrifices) is celebrated to commemorate the obedience of Hazrat Ibrahim^(as) and his son Hazrat Ismail^(as) to the commandment of Allah. Hazrat Ibrahim^(as) 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. Hazrat 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 (saw).

On the day of Eid those Muslims who can afford to sacrifice an animal are enjoined to do so after Eid Prayer. Following Takbeeraat should be repeated on the Eid Day.

Allaho Akbar Allaho Akbar
La Ilaha Illallaho
Wallaho Akbar Allaho Akbar
Wa Lillahil hamdAllah is the Greatest, Allah is the Greatest;
there is no God beside Allah;
Allah is the Greatest, Allah is the Greatest,
and all praise belongs to Allah.