佛說盂蘭盆經疏 2.38

2.38

問：五百生慳，為人為鬼？答：人鬼相間，造受相資。若唯人身不名惡報，若唯鬼身不應造業。或亦為畜，於理無妨。但慳習不除，即名相續。

Question: In those five hundred lifetimes of stinginess, was she human or ghost? Answer: Humans and ghosts alternated; creating [karma] and receiving [retribution] supported each other. If it were only human rebirths, it would not be called evil retribution; if it were only ghost rebirths, she would not have created karma. Or she may have been an animal; in principle there is no obstacle to this. As long as the habit of stinginess was not eradicated, it is termed continuous.