Keritot, Chapter Six, Mishnah Three
In this mishnah Rabbi Eliezer and the sages debate whether one can/should bring an asham talui every day.
1) Rabbi Eliezer says: one may freely offer an asham talui every day and at any time he pleases and such a sacrifice is called the asham of the pious.
2) They said of Bava ben Buti that he used to freely offer an asham talui every day, except on the day after Yom Kippur.
a) He declared: By this temple! Had they allowed me, I would have offered one even then, but they said to me, wait until you have come to a state of doubt.
3) But the sages say one may not bring an asham talui except for a sin that [is punished by] karet [when done intentionally and for which one brings a hatat [when done unwittingly.
Section one: Rabbi Eliezer holds that one can freely offer an asham talui whenever he wants, even if he doesnt know that he has sinned. This differs from the rules concerning a hatat. A hatat can be brought only by one who knows that he sinned, because a hatat must effect atonement. In contrast, according to Rabbi Eliezer, the asham talui does not really effect atonement, because when the person finds out that he actually sinned, he must bring a hatat. This is evidence that the asham talui is really just a freewill offering. Note that this matches his opinion in mishnah one.
This asham is called the asham of the pious (hasid) because one brings it just in case he sins.
Section two: The mishnah now relates the story of Bava ben Buti who would bring an asham talui every day (besides being pious, he must have been quite rich) except for the day after Yom Kippur. Since Yom Kippur atones for all sins, and certainly for ones which a person doesnt even know if he committed, he didnt need to bring it that one day. But, he goes on to say that he wanted to bring an asham talui that day as well. The other sages seem to have convinced him that he shouldnt do so until there is at least a chance that he sinned. It is possible that the other sages worried that if he would bring an asham talui on the day after Yom Kippur, people would think that Yom Kippur doesnt atone. Therefore, they opposed his doing so.
Section three: The other sages reject Rabbi Eliezer. They hold that one can bring an asham talui only if he thinks he might have committed a sin for which he would be liable for karet if done intentionally or a hatat if done unwittingly. He cannot simply freely donate an asham talui out of piety.