Eid al-Adha, (known elsewhere as Eidi Korbon and meaning the 'Festival of Sacrifice') commemorates the story of Abraham's test of faith and the substitution of a ram in place of Abraham's son as a sacrifice to God.
The Qur'an offers a summary of the story in Surah as-Saffat:
The following is the story of Eid al-Adha, as told to the prophet Musa and recorded in the first book of the Tawrat, Genesis. You can also read an esoteric interpretation *here*
Genesis 22:1-19
After these things God tested Abraham and said to him, “Abraham!” And he said, “Here I am.”