Muslims around the world are celebrating Eid al-Adha, the Muslim festival of sacrifice, which began on Tuesday and continues until the end of the Hajj pilgrimage.

The festival, one of the two most important Muslim feasts, starts on the tenth day of the last Islamic month on the calendar, Dhu al-Hijjah. Many Muslims wait for authorities in Mecca, the Fiqh Council, to announce the official day, which was determined to be Tuesday this year.

Eid al-Adha commemorates the Prophet Ibrahim’s sacrifice of his son, Ishmael, to Allah as an act of obedience. Allah spared Ishmael after seeing Ibrahim's devotion and instead gave him a sheep to kill. In the Bible version, he is named Abraham and it is Isaac, not Ishmael, who is almost sacrificed.

The three-day festival also marks the end of Hajj, the annual pilgrimage to Mecca in Saudi Arabia, Prophet Muhammad's birthplace. Muslims are expected to make the pilgrimage once in their lifetimes.

On the Eid, many Muslims celebrate and pay tribute to Allah, who gave mercy to Ibrahim, going to a mosque for morning prayers followed by slaughtering animals. Much of the meat is given away to others as a symbol of Muslim’s willingness to give up on behalf of Allah’s command. The sacrificed animal is cut in thirds, with one third eaten in a celebratory dinner by family, one third offered to friends, and the remaining portion donated to those less fortunate.

Worshipers of the holiday typically wish each other “Eid Mubarak,” which is the standard greeting during observance of Eid al-Adha, meaning “Have a blessed Eid.”