Reference for Keritot 37:20

כאן עשו אבל בכל התורה כולה לא מאי טעמא

to teach us that one is liable both for forgetfulness of th uncleanness and for forgetfulness of the Temple.<span class="x" onmousemove="('comment',' Shebu. 14b. The term 'hidden' is the source of the rule that knowledge at one time of the uncleanness is essential, cf. Shebu. 4a. As R. Ishmael uses this expression to derive another law, it may be assumed that he disagrees with that rule, and does not require knowledge in the beginning.');">⁸</span>

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