Reference for Zevachim 65:6

איכא דאמרי אמר רב יוסף כל הסומך ראשו ורובו מכניס מאי טעמא כל כחו בעינן הלכך לא אפשר

Others state [that] R'Joseph said: When one lays [hands], he must project his head and the greater part [of his body into the Temple court].<span class="x" onmousemove="('comment',' So that it would not be partial entry but complete entry, which is forbidden to the leper.');">¹¹</span> What is the reason? - We require [him to lay hands with] all his strength; therefore it cannot be done [otherwise].

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