法苑珠林 6.122

6.122

述曰。數見愚俗邪說之人云。貴賤不同人畜殊別。何有人作畜生畜生。作人。佛說虛誑恐不依實。若汝守愚不信佛言者。何故。前列俗典書史具述。目驗所覩豈亦不信。如行恩含忍。即同楚子蛭痼疾皆愈。宋公不禱妖星夕退。若也行惡如漢鴆趙王如意。蒼狗成肉。齊殺彭生立豕為祟。近事尚然。況復行因善惡業報。昇沈殊趣累劫受殃也。

The author remarks: I have often seen foolish and worldly people of perverse speech say, 'The noble and base are not alike; humans and beasts are completely different. How could a human become an animal, or an animal become a human? What the Buddha said is false and deceptive, perhaps not based on reality.' If you cling to ignorance and do not believe the Buddha's words, why is it that in the aforementioned mundane texts, records, and histories, things witnessed by eyes are fully set forth—could you disbelieve those as well? If one practices grace and forbearance, it is like the Viscount of Chu swallowing the leech and his chronic illness was completely healed, or Duke of Song not praying and the ominous star retreated that evening. If one commits evil, it is like the poisoning of Ruyi, Prince of Zhao, in the Han dynasty, where the blue dog turned into meat, or the killing of Pengsheng in Qi, who stood up as a pig to cause a haunting. Even recent worldly affairs are like this, how much more so with the karmic retributions of practicing good and evil causes, ascending or sinking into different destinies, suffering calamity for cumulative kalpas!