Horayot, Chapter Two, Mishnah One
Leviticus 4:3 states, If it is the anointed priest who has incurred guilt, so that blame falls upon the people, he shall offer for the sin of which he is guilty a bull of the herd without blemish as a sin offering to the Lord. According to the rabbis, this verse refers to a high priest who issues an errant ruling to himself. If he acts according to his errant ruling then he is not treated as if he was an individual who would have to bring a regular goat sin offering. Rather in his ruling he is considered parallel to the court and in his acting he is parallel to a community, much in the same way we learned above in mishnah 1:4. Our mishnah, and the mishnayoth that follow it, takes some of the rules that apply when a court rules and the congregation sins in error, and applies them to the high priest.
I) An anointed priest who rendered a decision for himself in error and acted unwittingly accordingly, must bring a bull.
II) If he rendered the decision in error but acted upon it willfully, or made it willfully but acted upon it unwittingly, he is exempt; for a decision a high priest made for himself is like a ruling issued by the court to the community.
If the high priest ruled that something was permitted, and in reality it was punishable by kareth (if done willfully) or the transgression causes one to be liable to bring a sin offering (if done unwittingly) and then he acted upon his ruling, without realizing that he is transgressing, he must bring a bull as a sin offering. In other words, instead of being just an individual who unwittingly transgresses and therefore brings a goat as a sin offering, the high priest brings a bull.
If, however, either the ruling was in error but the action was an intentional transgression, or vice versa, the ruling was intentionally wrong, but the action was unwitting, he is not liable to bring the bull. As we learned at the end of mishnah four, both the ruling and the act must be done unwittingly for the court, or in this case the high priest to be liable to bring a bull.