Practitioners who do not wear silk, leather boots, furs, or down, or consume milk, cream, or butter can truly transcend this world. When they have experienced the consequences of their previous acts, they will not have to re-enter the Triple Realm. […]
Both physically and mentally one must avoid the bodies and the by-products of living beings, by neither wearing them nor eating them. I say that such people have true liberation.
What I have said here is the teaching of the Buddhas. Any explanation counter to it is the teaching of demons.
—Buddha Shakyamuni, Surangama Sutra 6:27-29