Reference for Niddah 37:22

וכמימי אדמה

and in connection with this Rabbah explained: It is as though [the spot] darkened<span class="x" onmousemove="('comment',' Cf. If the plague be dim (or dark)&nbsp;… then the priest shall pronounce him clean (Lev. XIII, 6). ');">¹⁸</span>

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