Introduction Mishnah two discusses burning the hides of sacrificially unfit animals.
Rabbi Hanina, chief of the priests, said: “All my days I never saw a hide taken out to the place of burning.” Rabbi Akiba said: “From his words we infer that whoever flays the hide of the firstborn beast and it is found to be trefah, the priests may enjoy the use of the hide.” But the Sages say: “[A testimony which consists of] ‘we didn’t see’ is not a proof; rather the hide must be taken out to the place of burning. In Tractate Zevahim 12:4 the Mishnah teaches that if a sacrificial animal is found to be unfit as a sacrifice before it’s hide is flayed, the entire animal must be burnt. If it is found to be unfit after it’s hide is flayed, the priests may keep the hide. Rabbi Hanina testifies that he never saw a hide being burnt. In other words, according to Rabbi Hanina if they already removed the hide, the priests may make use of it, even though the animal was deemed unfit to be a sacrifice. Rabbi Akiva learns from this that if one flays the hide of a firstborn animal, which belongs to the priests, and then discovers that it was a trefah, an animal with an internal flaw that would have caused its death, the priests may keep the hide. Since the flaw was not known before the hide was removed, the hide becomes the property of the priests. The Sages respond to Rabbi Akiva that the type of testimony that Rabbi Hanina transmitted is not reliable enough to base upon it halakhic solutions. Not seeing something does not mean that it did not happen. Since they exclude Rabbi Hanina’s testimony the law is that the hide must be burnt with the rest of the animal, and the priests are forbidden to receive benefit from it.