The Bodhisatta was once an ascetic who lived in the Himalayas. One time while down in a town to get salt and seasoning he went on an alms round and a rich man decided to annoy him. He took the Bodhisatta to his house and served him a meal with fish. When the meal was over the rich man told the Bodhisatta he had killed the fish especially for him and accused the Bodhisatta of doing wrong by eating it. The Bodhisatta answered that only the killing is wrong, it is okay to eat any food given by people.
In the Lifetime of the Buddha
The rich man who hassled the Bodhisatta was an earlier birth of a prominent ascetic who opposed the Buddha. One time after a general had converted to Buddhism he offered a large meal to the Buddha that included meat. When the heretic ascetic found out about this he went around criticizing the Buddha for knowingly accepting and eating the meat.
Later when he heard some of his disciples discussing this, the Buddha told them this story so they knew that this ascetic had made the same spiteful, errant attack in the past.