Reference for Bekhorot 40:18

יצאה מליאה חוששת ר' יהושע אומר אינה חוששת

had a mother-in-law, she need not fear,<span class="x" onmousemove="('comment',' Lest meanwhile, during their absence, the mother-in-law had given birth to a son whom the widow is now obliged under the levirate law to marry.');">⁹</span>

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