Eid-Ul-Azha

Eid-Ul-Azha is a a Holly and joyful event for the Muslims. It is celebrated to to honour the willingness of the Prophet Ibrahim (Pbh) to sacrifice his young first-born son Ismail (Pbh) as an act of submission to Allah's command and his son's acceptance to being sacrificed, before God intervened to provide Prophet Ibrahim (Pbh) with a ram to sacrifice instead. In the lunar Islamic calendar, Eid al-Adha falls on the 10th day of Dhu al-Hijjah and lasts for four days.

Now people sacrifice Cow, Goat, Ram or Camel to Allah, for honoring the sacrifice of Prophet Ibrahim (Pbh) and Ismail (Pbh). But all that matters is devotion towards Allah rather than anything else.