Ordinarily, a sin-offering is brought when a person performs a forbidden act accidentally. There is another korban, an asham taluy, which is a sacrifice brought by someone who is uncertain as to whether he committed a sin that requires a sin-offering (see Vayikra 5:17-18). The Gemara on today’s daf (=page) discusses a case where someone set aside an animal to be brought as an asham taluy, but before it is offered, he learns definitively that he did not commit the sin. Three opinions appear in the baraita that is brought by our Gemara.
Rabbi Me’ir rules that once the owner has learned that he did not commit the sin, it is clear that the sacrifice was brought in error. He can, therefore, return the animal to the herd without redeeming it.
According to the Hakhamim, we treat it like any sacrifice that cannot be brought. That is, we leave it on its own until it becomes blemished in a manner that precludes it from being brought as a sacrifice. At that time it can be redeemed, and the money will be given to the Temple to use for another sacrifice.
Rabbi Eliezer says that the animal should nonetheless be offered as an asham taluy. His argument is that although he knows that he does not need to bring a sacrifice for this sin, it will serve as an atonement for some other sin that he no doubt did at some point in his life.
In the Gemara in Masechet Keritot (l7b-18a) the Sages debate the precise definition of the doubt which requires bringing an asham taluy sacrifice. During the Second Temple period, it was commonly offered even by individuals who had no real doubt, but merely a slight suspicion that they had committed a sin. Therefore, it was also called the guilt-offering of the pious.