Reference for Niddah 64:8

אבל זבה דאי חזאי חד יומא בשומרת יום כנגד יום סגי לה אימא

— It was necessary. For if the All Merciful had written the law in regard to a menstruant only it might have been presumed that it applied only to the menstruant, since even if she observed a discharge on one day only she must continue unclean for seven days, but not to a zabah for whom, if she observed a discharge<span class="x" onmousemove="('comment',' After the seven days of menstruation. ');">⁷</span>

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