Reference for Niddah 71:20

תא שמע

she should have become unclean for twenty-four hours retrospectively? — This is a case where there was not time enough.<span class="x" onmousemove="('comment',' Sc. less than a twenty-four hours interval has elapsed between the end of the clean period and the observation of the discharge. Hence even if the blood discharged had been in the outer chamber twenty-four hours previously the woman (since her blood at that time was still clean) could not be deemed unclean. ');">¹⁸</span>

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