Reference for Niddah 29:14

וכי תימא

but not on account of his intercourse.<span class="x" onmousemove="('comment',' With a menstruant; sc. the uncleanness, even in its uncertain character, does not extend over seven days as would have been the case with one who had intercourse with a confirmed menstruant. ');">¹⁴</span>

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