TT #32 · Parshas Shemini · Aliyah 2 · Passuk 22
Chabad.org — English translation + Rashi
English: “He descended from making”: Rabbi Yehoshua ben Levi teaches that a priest who does not ascend the platform for the priestly blessing during the service does not ascend it later; Aaron’s blessing and descent provide the model.
Sotah 38b.
E-Daf.com — Sotah 38b (Tsurras Hadaf)
Textual analogy — Aaron’s descent from the service is used as the model for the priest who has completed the Temple service.
The priestly blessing is tied to the service, yielding the rule that a priest who did not ascend for blessing during the service does not later ascend.