This year, the Muslim world celebrates the feast of Kurban Bayram on December 8th. The feast goes on for 10 days and is connected to the holy sacrifice of an animal, according to the requirements of the Koran "Pray to your Lord and make a sacrifice"..
That feast originates from the Biblical legend of the arch-father Abraham (Ibrahim in Islam), his wife Hagar and their son Isaac's (Ismail in Islam) being offered for sacrifice. The apologue of Ibrahim and Ismail, emergence of ancient Arabic sanctuaries of Mecca, rituals of peregrination to Mecca and the associated feast of sacrifice got new interpretation in the course of time and were subjected to requirements of Islam.
According to it, Allah is willing to these rituals to be performed in Mecca and its environs, and in connection with this the traditional peregrination to Mecca (Haj) has been established. This city had been the destination of peregrination for Arabs and a major religious center of Western Arabia. The resident tribes of Arabia (kureyshits etc.) celebrated their holidays and performed their rites at the sanctuary of Kaaba, they sacrificed to the heathen gods, making human immolations also.
Kurban Bayrami, various associated rites, and peregrination to Mecca are the remnants of these primitive beliefs. Before Islam the date of Kurban Bayrami were fixed - it was Zel-hijje month of immovable calendar of ancient Arabs. With Muslim calendar introduced, this holiday came to be celebrated at different days every year.
For more info on the feast - go here, here or here