Eid al-Adha is the latter of two Eid festivals celebrated by Muslims, whose basis comes from Sura 2 (Al-Baqara) Ayah 196 in the Qur'an. Like Eid ul-Fitr, Eid al-Adha begins with a Wajib prayer of two Raka'ah (units) followed by a sermon (khuṭbah).
The word "Eid" appears in Sura al-Mai'da ("The Table Spread," Chapter 5) of the Qur'an, meaning 'solemn festival'.
Eid al-Adha is celebrated annually on the 10th day of the 12th and the last Islamic month of Dhu al-Hijjah (ذو الحجة) of the lunar Islamic calendar.[4] Eid al-Adha celebrations start after the Hajj, the annual pilgrimage to Mecca in Saudi Arabia by Muslims worldwide, descend from Mount Arafat. The date is approximately 70 days (2 Months & 10 days) after the end of the month of Ramadan, i.e. Eid-ul-Fitr. Ritual observance of the holiday lasts until sunset of the 13th day of Dhu al-Hijjah.
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[http://en.wikipedia.org/wiki/Eid_al-Adha]