Bekhorot 35A

טימא טהרות ומת ⁠— לא קנסו בנו אחריו. מאי טעמא? היזק שאינו ניכר לא שמיה היזק, קנסא דרבנן ⁠— לדידיה קנסו רבנן, לבריה לא קנסו רבנן.

that if one rendered impure the ritually pure items of another and died before paying, the rabbis did not penalize his son after his death and require him to pay for the damage. What is the reason for this? The reason is that damage that is not evident, i.e., which does not involve any visible change, is not considered damage by Torah law. There is a penalty imposed by rabbinic law, as the injured party suffered a loss, but the rabbis penalized only him; the rabbis did not penalize his son.

מתני׳ מעשה בזכר של רחלים זקן, ושערו מדולדל, וראהו קסטור אחד ואמר: מה טיבו של זה? אמרו לו: בכור הוא, ואינו נשחט אלא אם כן היה בו מום. נטל (פיגום) [פיגיום] וצרם אזנו, ובא מעשה לפני חכמים והתירו, ואחר שהתירו הלך וצירם באזני בכורות אחרים ואסרו.

Mishnah: There was an incident involving an old ram whose hair was long and dangling, because it was a firstborn offering. And one Roman quaestor [kastor] saw it and said to its owner: What is the status [tivo] of this animal that you allowed it to grow old and you did not slaughter it? They said to him: It is a firstborn offering, and therefore it may be slaughtered only if it has a blemish. The quaestor took a dagger [pigom] and slit its ear. And the incident came before the rabbis for a ruling, and they deemed its slaughter permitted. And after the rabbis deemed its slaughter permitted, the quaestor went and slit the ears of other firstborn offerings, but in these cases the rabbis deemed their slaughter prohibited, despite the fact that they were now blemished.

פעם אחת היו תינוקות משחקין בשדה, וקשרו זנבי טלאים זה בזה, ונפסקה זנבו של אחד מהם, והרי הוא בכור, ובא מעשה לפני חכמים והתירו. ראו שהתירו, הלכו וקשרו זנבות בכורות אחרים, ואסרו. זה הכלל: כל שהוא לדעתו ⁠— אסור, שלא לדעתו ⁠— מותר.

One time children were playing in the field and they tied the tails of lambs to each other, and the tail of one of them was severed, and it was a firstborn offering. And the incident came before the rabbis for a ruling and they deemed its slaughter permitted. The people who saw that they deemed its slaughter permitted went and tied the tails of other firstborn offerings, and the rabbis deemed their slaughter prohibited. This is the principle: With regard to any blemish that is caused intentionally, the animal’s slaughter is prohibited; if the blemish is caused unintentionally, the animal’s slaughter is permitted.