Reference for Niddah 41:43

אלא אמר רב נחמן בר יצחק

who also stated, '[If it had the colour] of one of the four kinds of blood all agree that she is unclean', [the additional difficulty arises:] Were not red and black also mentioned and the Rabbis nevertheless differ.<span class="x" onmousemove="('comment',' From R. Judah and declare it clean. ');">³⁷</span>

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