Chabad.org — English translation + Rashi
Torah Temimah points to Horayos 10a.
E-Daf.com — Horayos 10a
HebrewBooks / Shas PDF
English: “And he shall offer for his sin that he has sinned” — this teaches that he brings a bull for his past sin; from here that an anointed kohen who sinned and [then] left office…
Atonement for past office-sin — a High Priest who sinned while in office and later left still brings the bull for that earlier sin.
A High Priest who sinned while in office and later left still brings the bull for that earlier sin. The verse’s language “for his sin that he has sinned” is read as covering the past act even after the office has ended. The special chatas therefore remains attached to the sin of the office-holder rather than dissolving with the termination of the appointment.