Hullin, Chapter Five, Mishnah Three
1) If a person slaughtered [an animal] and it was found to be terefah, or if he slaughtered [it as an offering] to idols, or if he slaughtered the red cow, or an ox which was condemned to be stoned, or a heifer whose neck was to be broken:
a) Rabbi Shimon exempts [him from having transgressed the law of it and its young];
b) But the sages make him liable.
2) If a person slaughtered [an animal] and it became nevelah under his hand, or if he stabbed it, or tore away [the organs of the throat], he does not thereby transgress the law of it and its young.
3) If two people bought a cow and its young, he who bought first can slaughter first; but if the second preceded him, he holds his advantage.
4) If a person slaughtered a cow and then two of its calves, he is liable for eighty lashes.
a) If he slaughtered its two calves and then the cow, he is liable for forty lashes.
b) If he slaughtered it and then its calf and then the calf’s offspring, he is liable for eighty lashes.
c) If he slaughtered it and then its calf’s offspring and then the calf, he is liable for forty lashes.
d) Symmachos says in the name of r. Meir: he is liable for eighty lashes.
5) At four periods in the year he who sells a beast to another must inform him, I sold today its mother to be slaughtered, or I sold today its young to be slaughtered, and these are they: on the eve of the last day of the feast [of Sukkot], on the eve of the first day of Pesah, on the eve of Shavuot, and on the eve of Rosh Hashanah.
a) According to Rabbi Yose the Galilean, also on the eve of Yom Kippur, in the Galilee.
b) Rabbi Judah says, this is so, only when there was no time in between the sales, but if there was time, he need not inform him.
c) Rabbi Judah agrees that if he sold the mother to the bridegroom and the young to the bride, he must inform them of it, for it is certain that they will each slaughter on the same day.
Section one: In all of these cases a person slaughters a parent and its offspring on the same day, but one of the animals was an animal that could not be eaten. There are five such categories:
1) A terefah, an animal that has a flaw that will cause it to eminently die.
2) An animal slaughtered for idolatry.
3) The red cow, used for purifying people with corpse impurity.
4) An ox condemned to die for either killing a person or for engaging in bestiality. It is forbidden to derive benefit from such an ox.
5) The heifer whose neck is broken to atone for an unsolved murder.
Since these animals can not be eaten, even if they were slaughtered properly, Rabbi Shimon exempts the one who slaughters the second one from being liable for it and its son. Rabbi Shimon holds that slaughtering that would not make an animal fit for consumption even if done properly is not called slaughtering. The other rabbis disagree and say that he is liable, since he did indeed slaughter the second animal.
Section two: In this case, the animal was valid before it was slaughtered, but then was invalidated by an improper method of slaughtering. Such a person is not liable for transgressing it and its son because this prohibition only applies to one who slaughters, the verb used in the verse. This person did not successfully slaughter.
Section three: If two people buy a cow and its young, they might end up arguing about who has the right to slaughter first. The mishnah says that the first person to buy has the right to slaughter first, and the second person should wait. But if the second person slaughters first, the other person will have to wait for the next day.
Section four: This section attempts to delineate how many transgressions a person has transgressed when he slaughters multiple animals on the same day. We will take case by case.
1) Once he slaughters the mother, he will be liable for each of its offspring that he slaughters on that day. Therefore, when he slaughters two offspring, he is liable twice.
2) However, if he slaughters two offspring and then the mother, he has violated the prohibition only once, by slaughtering the mother. In other words, we dont count his transgressions retroactively.
3) When he slaughters the mother, it is prohibited to slaughter its young. So when he slaughters the young, he is liable for forty lashes. When he slaughters the offspring of the young, he has violated the prohibition again, and is liable for another forty lashes (ouch!)
4) If after slaughtering the mother, he first slaughters the offspring of the mothers offspring (the third generation), and then the mothers own offspring, according to the first opinion, he has only transgressed once. Slaughtering the third generation was not prohibited at the time that he slaughtered it. And although slaughtering the second generation violated two prohibitions, for it is the mother of the third generation and the child of the first generation, one can be liable only once for each animal.
Rabbi Meir holds that he is liable twice, even though he slaughtered only one prohibited animal, since that one animal was prohibited in two different ways.
Section five: When a merchant sells an animal and then sells its mother/offspring to different customers there might be a concern that the two people will slaughter the animals on the same day and thereby unwittingly the prohibition of it and its son. This will only be a concern if it is anticipated that a person who buys an animal will slaughter it on that very day. The mishnah informs us that this is a strong possibility four times a year, the four times when people ate the most meat. The four times are as follows:
1) Before the last day of Sukkot, which we call Shemini Atzeret. Interestingly, people seem to have eaten more meat on the last day of Sukkot then on the first day. This might be connected with Simchat Bet Hashoevah, the celebration described in the end of tractate Sukkah.
2) Before the first day of Pesah. People would have eaten meat for the Pesah meal (the seder) both before and after the destruction of the Temple.
3) Before Shavuot.
4) Before Rosh Hashanah.
Rabbi Yose the Galilean notes that in the Galilee the same rule would hold the day before Yom Kippur. In the Galilee they ate large meat meals before the onset of the fast.
Rabbi Judah limits the law to a case where there was not a day separating the sale of the mother and its young. If there was a day separating the sales, then the seller need not inform him. According to Rabbi Judah, two different buyers buying on two different days are not likely to slaughter on the same day.
There is a case where Rabbi Judah agrees that even if the sales occur on two different days, the seller must inform the purchasers. If a bride and bridegroom buy a mother and its young, he must inform them, because it is clear that they will be slaughtered on the same day.