Reference for Niddah 48:4

יצא מי שיש לו ב' גבין וב' שדראות דאע"ג דכלו לו חדשיו אם יצא לאויר העולם אסור במעי אמו שרי

A Tanna recited before Rab: As it might have been assumed that if an abortion was a creature with a shapeless body or with a shapeless head its mother is unclean by reason of its birth, it was explicitly stated in Scripture, If a woman be delivered, and bear a man-child etc.<span class="x" onmousemove="('comment',' She shall be unclean. Lev. XII, 2. ');">⁴</span>

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