Reference for Niddah 74:11

ורבא הא מני רבי אליעזר היא דאמר מסתר נמי סתרה

From what was taught: As are the days of her menstruation so are the days of her bearing. As the days of her menstruation are not suitable [for counting as the days] after her <i>zibah</i><span class="x" onmousemove="('comment',' Since the zibah period follows that of menstruation and not vice versa, while a subsequent menstruation period cannot begin before seven clean days have passed after the zibah had ceased. ');">¹⁰</span>

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