Animal sacrifices mentioned in the suttas or vinaya? Hindus believe that the Buddha opposed Vedic rites of animal sacrifice in his time, for example, on this page and on this page.
This apparently influenced later Hindus to abandon the practice of animal sacrifice.
In the suttas, we find the Buddha forbidding taking of a life, and this is the first precept.
But are there any sutta or vinaya references showing the Buddha explicitly opposing animal sacrifices as a religious practice?
AN 4.39, AN 4.40, DN 5 and also see MN 55

Then Ujjaya the brahmin went up to the Buddha, and exchanged greetings with him. When the greetings and polite conversation were over, he sat down to one side and said to the Buddha:
“Does Master Gotama praise sacrifice?”
“Brahmin, I don’t praise all sacrifices. Nor do I criticize all sacrifices. Take the kind of sacrifice where cattle, goats and sheep, chickens and pigs, and various kinds of creatures are slaughtered. I criticize that kind of violent sacrifice. Why is that? Because neither perfected ones nor those who have entered the path to perfection will attend such a violent sacrifice.
But take the kind of sacrifice where cattle, goats and sheep, chickens and pigs, and various kinds of creatures are not slaughtered. I praise that kind of non-violent sacrifice; for example, a regular gift as an ongoing family sacrifice. Why is that? Because perfected ones and those who have entered the path to perfection will attend such a non-violent sacrifice. [AN4.39]

Also see: [DN 5]