法苑珠林 23.44

23.44

又四品學經云。凡俗之人。或有不如畜生。畜生或勝於人。所以者何。人作罪不止死入地獄。罪畢始為餓鬼。餓鬼罪畢轉為畜生。畜生罪畢乃還為人。以畜生中畢罪便得為人。是故當作善奉三尊之教。長離三惡道。受天人福後長解脫。

Furthermore, the Sūtra on the Four Grades of Study says: Ordinary worldly folk may sometimes be inferior to beasts, and beasts may sometimes surpass humans. Why is this? If a human commits offenses without stopping, upon death he enters hell; when the retribution for his offenses is finished, he only then becomes a hungry ghost; when the offenses of the hungry ghost are finished, he changes into a beast; when the offenses of the beast are finished, he then returns to human form. Because he finishes his offenses while among beasts, he then attains human form. Therefore, one should do good and honor the teachings of the Three Honored Ones, departing forever from the three evil destinies, enjoying the blessings of devas and humans, and ultimately attaining everlasting liberation.