I was just reading about livestock sacrifice during Eid ul-Adha, prompted by seeing it on Muslim charity sites, such as Muslim Aid Australia.
Affluent Muslims who can afford it sacrifice their best halal domestic animals (usually a cow, but can also be a camel, goat, sheep, or ram depending on the region) as a symbol of Abraham's willingness to sacrifice his only son. The sacrificed animals, called aḍḥiya (Arabic: أضحية), known also by the Perso-Arabic term qurbāni, have to meet certain age and quality standards or else the animal is considered an unacceptable sacrifice. -- Eid al-Adha, Wikipedia
Qurbāni is the sacrifice of a livestock animal during Eid al-Adha. -- Qurbani, Wikipedia
I hear it's symbolic of Prophet Abraham's sacrifice of his son (Qur'an 37:100-112). I've seen several conflicting claims about what happens next (God gave him a sheep to sacrifice instead; God substituted a ram in Ismail's place; either the knife is turned over in his hand or copper appears on Ishmael), but the Qur'an says:
And when they had both submitted and he put him down upon his forehead, We called to him, "O Abraham, You have fulfilled the vision." Indeed, We thus reward the doers of good. -- Qur'an 37:103-105
And I don't see mention of an animal (or anything) being killed.
Every year, thousands of animals are sacrificed by Muslims. It is, in a sense, a symbolic expression that a Muslim can sacrifice anything he has in order to worship Allah, comply with His command and give up anything he has for His sake. -- Questions on Islam
I'm a vegetarian, so I'm hesistant to play a role in killing an animal. Moreover, the Qur'an says they had both submitted (Abraham and his son), whereas an animal cannot agree to its own sacrifice. (It seems I'm not the only one uncomfortable with this: see Giving money instead of buying an animal and Celebration of Eid ul Adha for a vegan muslim). So I'm trying to figure out where the idea of livestock sacrifice came from.
Question: What is the origin of livestock sacrifice for Eid ul-Adha?