In Mecca, Islam's holiest city, pilgrims who have just completed their Hajj began the day with prayers in al-Masjid al-Haram, the world's largest mosque. After prayers, pilgrims perform the 'tawaf'- circling the Islamic shrine of Kaaba seven times - and then head for the valley of Mina 5 km (3 miles) east of the city, the historic site for sacrificing animals.
In 632 Prophet Muhammad declared the valley Allah's table and sacrificed 63 camels as an offering there.
King Abdullah bin Abdul-Aziz and Crown Prince Sultan bin Abdul-Aziz also attended, as well as Iranian President Mahmoud Ahmadinejad, who preformed the hajj at the king's personal invitation.
All Muslims who can afford it must kill an animal during the festival to commemorate Ibrahim's sacrifice.
As a rule sheep, goats, camels and cows are killed. The animals should meet certain quality standards - goats should be six months of age, sheep - 12 months, camels and cattle - five and four years, respectively.
Islamic tradition prescribes Muslims eat, drink, have fun, pay and receive visits and show compassion to the poor, while fasting and fighting is strictly prohibited.