Muslims around the world are celebrating on Friday Eid al-Kabir, literally meaning the "great feast," which is also called Eid al-Adha (meaning the "feast of sacrifice").
The festival also corresponds to the end of pilgrimage to Mecca, the Hajj, which more than two million Muslims are attending this week.
Eid al-Adha is celebrated from the tenth day of the lunar month of dhou al hijja, and lasts three days.
It comes a day after pilgrims gathered at Mount Arafat on Thursday for a vigil to atone for their sins, then descended to Muzdalifa to prepare for the final stages of the annual hajj pilgrimage.
Pilgrims clad in white robes spent the previous night in an encampment at the hill where Islam holds that God tested Abraham's faith by commanding him to sacrifice his son Ismail and where the Prophet Mohammad gave his last sermon.
The date of Eid al-Adha moves by about eleven days earlier each year, because the difference in the Gregorian and Hijri calendars.
This festival, as important as Christmas is for Christians or Hanukkah is for Jews, is different from Eid el-Fitr, meaning "festival of the breaking of fast," which marks the end of the month of Ramadan earlier in the year.
Eid al-Adha marks the willingness of Ibrahim, or Abraham, to sacrifice his son on God's command.
As Ibrahim about to sacrifice his son Ismaeel, the angel Gabriel (or Jibril) stopped his gesture and replaced the child's body with a ram.
Muslims mark the holiday by slaughtering animals such as sheep and goats. The meat is shared among family, friends and especially donated to the poor.
In many societies and more specifically, one-third goes to family, one-third for friends and neighbors and one-third for the poor.
Traditionally, it was the head of the family who performed the sacrifice of the animal, but for sanitary and animal welfare reasons, ritual slaughter has become prohibited outside slaughterhouses around the world.
Faithful celebrate the first day of Eid by wearing their best clothes and gathering to pray special early morning prayers.
The expression "Eid Mubarak" is a greeting used to wish Muslims the best on the occasion.