Parashas Acharei Mos · Passuk 16:03
Chabad.org — English translation + Rashi
Torah Temima points to Yoma 50a.
English: “With a bull of the herd” — rather, with its blood: from here [we learn] that the blood is called “par”; therefore if the kohen slaughtered the bull and died before atoning with its blood, another kohen enters with this blood and atones with it.
Blood called “par”
The blood of the Yom Kippur bull may complete the service even if the original kohen dies after slaughter.