مسلم : Also written Id al'Adha (or Eid Al-Adha) is the Feast of the Sacrifice , the second main celebration of Islam.
It takes place on the tenth day of the twelfth -- last month of the Islamic calendar and celebrates Abraham's (also written Ibrahim) willingness to sacrifice his son in obedience to God. Muslims make their annual pilgrimage, or the Hajj , to Makkah (Mecca) in Saudi Arabia.
The Prophet Muhammad called Eid Al-Adha the best day of the year, since it is the last and biggest day of the annual pilgrimage.