References to cow sacrifices in veda-s
“In the Rigveda Saṃhitā, we see that our ancients cooked the flesh of oxen and offered it to the gods, especially Indra (see RVS 10.86.14 or 10.27.2, for example). Horses, bulls, oxen, barren cows, and rams were sacrificed for Agni (RVS 10.91.14). Śatapatha Brāhmaṇa 3.1.2.21 says that sage Yājñavalkya would eat the meat of cows and oxen, provided it was tender. Bṛhadāraṇyaka Upaniṣad 6.4.18 says that if a couple wants to beget a son who will grow up to be a great scholar, they have to eat rice cooked with beef, along with ghee. Śatapatha Brāhmaṇa 11.7.1.3 goes on to say that meat is the best kind of food!” … In RVS 8.43.11, Agni is hailed as one whose food is the ox and the barren cow. Often in the Rigveda Saṃhitā (see 1.164.27, 1.164.40, 4.1.6, and 5.83.8, for example), the cow is called aghnyā, ‘one who doesn’t deserve to be killed.’ Therefore, it seems that only barren cows were killed. How else do we account for the lavish praise showered on cows (RVS 6.23.1-8 and 8.101.15-16)? One verse (RVS 8.101.16), which hails the cow as devī, ‘goddess.’" SG15. - Bull to indra (10-28 -3 - unchecked)
References to animal sacrifice in other ancient works
“Brahma Sūtra (3.1.25) says that the scriptures don’t have a problem with killing animals for a specified ritual. Even the Manusmṛti, a text that is rather partial to vegetarianism, says that meat-eating is fine under specific circumstances like during a calamity or as part of a ritual (MS 5.27, 5.32)."SG15.
References in classical poetry
“In the Mahābhārata (Droṇa Parva / Book 3, Chapter 199), sage Mārkāṇḍeya tells Yudhiṣṭhira the story of a hunter and a priest. When the priest accuses the hunter of violence, the latter narrates the story of King Rantideva: “In Rantideva’s kitchen, two thousand animals were killed every day as were two thousand cows. Rantideva became famous because he fed meat to all his people."SG15.
" Kālidāsa (5th century CE) says in Meghadūta 1.45 that River Charmanvati (modern-day Chambal) arose from the glory of King Rantideva who sacrificed thousands of cows. Mallinātha (13th century CE) says in his commentary on the Meghadūta that Charmanvati originated with the constant washing of cow hide and the flowing of the blood of cows."SG15.