佛祖統紀 3.12

3.12

輔行引大論云。如來因地為鹿群主。波羅柰王入山遊獵。有母鹿懷子。當差次供饌。母告鹿主。枉殺其子。鹿主詣王求代。王說偈曰。我實人頭鹿。汝是鹿頭人。以理而為人。不以形為人。我從今日始。不食一切肉。我以無畏施。亦可安汝意。鹿群所居。故名鹿苑。亦名柰苑。從樹立名。亦名仙苑。二仙所住故。此以處標名酬昔行因之地。

The Fuxing quotes the Mahāprajñāpāramitopadeśa, which says, "When the Tathāgata was on the causal ground, he was the leader of a herd of deer. The king of Vārāṇasī entered the mountains to hunt. There was a doe carrying a fawn whose turn had come to be offered for food. The doe informed the deer leader that her fawn would be wrongfully killed. The deer leader went to the king to ask to take her place. The king spoke a verse: / 'I am truly a man with a deer's head; / You are a deer with a man's head. / By principle one is human, / Not by bodily form is one human. / Beginning from this day, / I shall not eat any meat. / By granting the gift of fearlessness, / I may also set your mind at ease.' / Because it was where the herd of deer resided, it is named the Deer Park. It is also called the Karaka Park, named after the trees. It is also called the Ṛṣi Park, because two ṛṣis lived there." This is designated by the place to recompense the site of his causal practices in the past.