Reference for Niddah 56:5

מ"ט

For we learnt: R. Eliezer stated, [It is written, If any one touch&nbsp;… the carcass of] unclean swarming things and&nbsp;… it being hidden from him,<span class="x" onmousemove="('comment',' Lev. V, 2. ');">⁹</span> one incurs the obligation of an offering only when the unclean swarming thing is hidden from him<span class="x" onmousemove="('comment',' Sc. when entering the Sanctuary the man forgot that he was unclean. ');">¹⁰</span>

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