Chabad.org — English translation + Rashi
Torah Temimah points to Kerisos 6b.
E-Daf.com — Kerisos 6b
HebrewBooks / Shas PDF
English: “A bull of the herd” — three years old.
Age of the High Priest’s bull — the chatas bull of the High Priest is three years old.
The chatas bull of the High Priest is three years old. The designation “par ben bakar” is understood to require a three-year-old animal. This age requirement distinguishes the High Priest’s bull from other offerings whose age parameters differ and fixes the precise animal that fulfills the verse’s command.