How can you eat the flesh of living beings and yet pretend to be my disciple? You should know that those who eat meat, though their minds may open and realize a semblance of meditation, are but great fiends who, after this life, will sink back into the bitter ocean of samsara and cannot follow the Path. They will kill and devour one another ceaselessly; how then can they escape from the three worlds of existence?
[…] How can those who practice great compassion feed on the flesh and blood of living beings? If you do not wear garments made of silk, boots of leather, and furs, and refrain from consuming milk, cream, and butter, you can truly be liberated from all worldly concerns. After paying your former debts, you will not transmigrate in the three realms of existence.
[…] If you can control your body and mind and thereby refrain from eating animal flesh and using animal products, I say you will really be liberated. This teaching of mine is that of the Buddha, whereas any other is that of the unholy.
—Buddha Shakyamuni, Surangama Sutra