Reference for Niddah 137:19

רב ככותאי אמרה לשמעתיה דאמרי יום שפוסקת בו סופרתו למנין ז'

'A menstruant'! What need has she for counting?<span class="x" onmousemove="('comment',' None, since a menstruant becomes clean after seven days irrespective of whether these were clean or not. ');">¹⁵</span>

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