Keritot, Chapter Six, Mishnah One
An asham talui is brought when a person is not sure if he has sinned. Our mishnah discussed what happens if after he brought it, he finds out that he did not sin (i.e. he ate the right piece of meat, or perhaps he had sex with his wife and not his sister).
1) If a person brought an asham talui and then found out that he did not sin:
a) If it was before the animal was slaughtered, it may go out to pasture among the flock, the words of Rabbi Meir.
b) The sages say: it goes out to pasture until it becomes blemished and it is then sold, and the money goes for freewill-offerings.
c) Rabbi Eliezer says: it shall be offered up, for if it does not expiate this sin, it will expiate another sin.
2) If he learns of it after it was slaughtered, the blood shall be spilled out and the flesh is removed to the place of burning.
3) If the blood had already been tossed [onto the altar], the flesh may be eaten.
a) Rabbi Yose says: even if the blood is still in the vessel, it should be tossed and the flesh then eaten.
Section one: If before the animal is slaughtered he finds out that he didnt sin, Rabbi Meir holds that the animal is not at all holy. It can go out to the flock with the rest of the hullin animals. The other sages say that it is holy and therefore it does not automatically revert to being hullin. However, it also cannot be sacrificed, because now it is not necessary. The solution is to let it go out to pasture until it becomes blemished. At this point the animal may be sold and he must use the money from the sale to buy freewill offerings.
Rabbi Eliezer assumes that a person might frequently commit sins which require expiation, and he might not even know that he has done so. Therefore, he can go ahead and sacrifice this asham talui, and it will expiate for other unknown sins. Note that the rest of the mishnah does not go according to Rabbi Eliezer.
Section two: If he learns that he didnt sin after the animal was already slaughtered, then the blood must be poured out into the aqueduct that runs through the Temple, and the flesh must be burned. In other words, it is a disqualified sacrifice.
Section three: Once the blood has been tossed onto the altar, the sacrifice is valid, even if it turns out that he didnt sin. The flesh can be eaten.
Rabbi Yose holds that once the blood is in the vessel, where it is put immediately after the animal is slaughtered, the sacrificial process can continue even if it turns out that the person didnt sin.