Vayikra 4:3

אם הכהן המשיח יחטא לאשמת העם IF THE PRIEST THAT IS ANOINTED DO SIN לאשמת העם — The Halachic explanation is that he is liable to bring a sin-offering only when there was ignorance of the real matter (of the law in question; i. e. after having considered the case in question he came to a wrong decision) together with a mistaken action (i. e. where he erred in a Halachic decision and as a result of this error acted against the true law), just as it is stated with reference to the guilt of the whole people): (v. 13) “[And if the whole congregation of Israel err] and the thing be hid from the eyes of the assembly and they have done [somewhat against the commandments of the Lord]" (Sifra, Vayikra Dibbura d'Chovah, Chapter 2 1; Horayot 7a; Rashi on v. 13). Its literal sense is according to the Agadic explanation: When the High-priest sins this is the guilt of the people (i. e. it results in the people remaining under a load of guilt), because they are dependent on him to effect atonement for them and to pray on their behalf, and now he himself has become degenerate and can thus not expiate for them, wherefor they remain under guilt. פר A BULLOCK — One might think that it may be an old one! Scripture, however, adds בן, a young animal. If, then, it must be בן, a young one, I might think a very young animal is fitted too (this being also implied in the term בן)! Scripture, however, states פר! How is this to be reconciled? By explaining פר בן בקר to be a bullock of three years (which is neither too old nor too young) (Sifra, Vayikra Dibbura d'Chovah, Chapter 3 1; cf. Rashi on Leviticus 9:7 and Note thereon).

אִ֣ם הַכֹּהֵ֧ן הַמָּשִׁ֛יחַ יֶחֱטָ֖א לְאַשְׁמַ֣ת הָעָ֑ם וְהִקְרִ֡יב עַ֣ל חַטָּאתוֹ֩ אֲשֶׁ֨ר חָטָ֜א פַּ֣ר בֶּן־בָּקָ֥ר תָּמִ֛ים לַיהֹוָ֖ה לְחַטָּֽאת׃

if the priest that is anointed do sin to bring guiltiness on the people; then let him bring for his sin, which he has sinned, a young bullock without blemish to the Lord for a sin offering.