Reference for Bekhorot 91:22

מי שהיו לו בנים ונשא אשה שלא ילדה

[INTIMATING] UNTIL THE OPENING OF THE WOMB IS '[OF THE CHILDREN] OF ISRAEL'.<span class="x" onmousemove="('comment',' It is only then that its birth is considered an opening of the womb to exempt future offspring from the law of redemption. The children therefore born when the woman was a gentile or a slave are not accounted as opening the womb.');">¹⁷</span>

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