Devadatta, who was a monk and the cousin of the Buddha, made a list of suggestions which the Buddha refused to make mandatory. The list by Devadatta included a list of ascetic type practices, including: (1) that monks should dwell all their lives in the forest, (2) that they should accept no invitations to meals, but live entirely on alms obtained by begging, (3) that they should wear only robes made of discarded rags and accept no robes from the laity, (4) that they should dwell at the foot of a tree and not under a roof, (5) that they should abstain completely from fish and flesh, even if it died naturally. Since the Buddha refused to accept this list, some teachers say that this shows the Buddha did not require or recommend vegetarianism.

But what these teachers fail to recognize is the Buddha allowed monks to follow the rules or suggestions by Devadatta, if they wanted to. It was not forbidden to follow the list, if a monk or nun wanted to. The refusal of the Buddha to accept the complete list also does not mean that he disagreed with everything in the list.

The Buddha praised Kassapa doing some ascetic practices (including wearing discarded rags, forest dwelling), some of them from the list of Devadatta (Samyutta Nikaya 16.5) which shows that the Buddha was not opposed to everything in the list.  In another passage the Buddha said:

"I do not say householder, that all asceticism should be practiced;  nor do I say of all asceticism that it should not be practiced"  (Anguttara Nikaya 10.94).