Mishnah Bekhorot 5

¹All dedicated animals which became unfit [for the altar] are sold in a market, slaughtered in a market and weighed by the liter, except for a first born or a tithed animal, as their profit goes to the owners, [whereas] the profit on dedicated objects which became unfit goes to the Temple. One can weigh one piece of meat of the first-born against another piece of ordinary meat. ²Bet Shammai says: An Israelite must not be invited to share [a blemished first born] with a priest. But Bet Hillel permits this, even in the case of a non-Jew. If a first born has a blood attack, even if it is going to die, its blood may not be let, the words of Rabbi Judah. But the sages say: he may let its blood, as long as he does not make a blemish. And if he made a blemish, he must not slaughter it on account of this. Rabbi Shimon says: he may let blood, even though he makes a blemish. ³If one makes a slit in the ear of a firstborn animal, he may never slaughter it, the words of Rabbi Eliezer. But the sages say: when another blemish appears, he may slaughter it on account of it. It happened that a quaestor (a Roman official) saw an old male lamb with its long wool hanging down and asked: what is the meaning of this? They replied: “It is a first born and is not to be slaughtered until it has a blemish,” [The quaestor] took a dagger and slit its ear. The matter came before the sages and they permitted it. After they had permitted, he went and sliced the ears of other [first borns]. The [sages] forbade them. Once children were once playing in a field. They tied the tails of sheep one to the other and one tail which belonged to a first born was severed. The matter came before the rabbis and they permitted [the first born]. When the children saw that they had permitted [the first born to be slaughtered], they proceeded to tie the tails of other first borns. The [sages] forbade [the other first borns]. This is the rule: wherever the blemish is caused with the knowledge and consent [of the owner] it is forbidden, but, if it is not with his knowledge and consent, it is permitted. ⁴If a first born was running after him and he kicked it and thereby blemished it, he may slaughter it on account of this. Any blemish which might have been made by a person, Israelite shepherds are trustworthy whereas shepherds who are priests are not trustworthy. Rabban Shimon ben Gamaliel says: he is trustworthy with regard to somebody else's first born, but he is not trustworthy with regard to his own. Rabbi Meir says: one who is suspected of neglecting a religious matter must not issue judgment on it or give evidence concerning it. ⁵A priest is trusted to say, “I have shown this first born [to an expert] and it is blemished.” All are trust worthy with regard to the blemishes of a tithed animal. A first born whose eye was blinded or whose fore-foot was cut off, or whose hind-leg was broken, may be slaughtered with the approval of three [persons] of the synagogue. But Rabbi Yose says: even if twenty-three were present, it must not be slaughtered except with the approval of an expert. ⁶If one slaughtered a first born and it became known that he had not shown it [to an expert]: That which [the purchasers] have eaten, they ate, and he must return the money to them. That which they have not yet eaten, the flesh must be buried and he must return the money to them. And likewise if one slaughtered a cow and sold it and it became known that it was terefah: That which [the purchasers] have eaten, they ate, and he must return the money to them. That which they have not eaten, they return the flesh to him and he must return the money to them. If [the purchasers], sold it to non-Jews or cast it to dogs, they must pay him the price of a terefah.