Tosefta for Yevamot 83:16
ותמתין שני חדשים ומחצה ותנשא דאי לשבעה ילדה האי בר שבעה לבתרא הוא ואי לשיתא ופלגא ילדה האי בר תשעה לקמא הוא דאי בר בתרא הוא בר שיתא ופלגא לא חיי
It is easy to understand why [a divorcee or widow] shall not marry after waiting a period of just two months because that would create a doubt as to whether the child is a nine-months one of the first<span class="x" onmousemove="('comment',' Husband. ');"><sup>27</sup></span> or a seven-months one of the second.<span class="x" onmousemove="('comment',' Husband. ');"><sup>27</sup></span>
Tosefta Niddah
A man may not marry a pregnant woman [who was impregnated] by his fellow, or a nursing woman [who is nursing the child] of his fellow, on account of that which is said (Prov. 23:10), "Do not remove ancient boundary stones; Do not encroach upon the field of orphans" (JPS tr.).
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