Reference for Zevachim 28:12

ולאו כל דכן הוא ומה הולכת אברים לכבש דלא מעכבא כפרה בעיא כהונה הולכת דם דמעכבא כפרה [לא כ"ש] (מיבעיא)

- Said R'Shisha the son of R'Idi: Let it be analogous to the inspection of [leprous] plagues, which is not a service, and yet requires the priesthood.<span class="x" onmousemove="('comment',' And likewise with the red heifer, being of the holy things of the Temple repair, the slaughtering thereof is not deemed in the category of Temple services, and the requirement of a priest is a special feature of the ritual connected therewith,');">⁷</span>

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