Reference for Niddah 127:35

היתה למודה להיות רואה יום חמשה עשר ושינתה ליום עשרים זה וזה אסורין

day of the month, she has not established for herself a settled period.<span class="x" onmousemove="('comment',' Since the difference between the dates of the first and the second month was only one day while that between the second and the third was two days. ');">³²</span>

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