Reference for Sanhedrin 151:5

אמר אביי אמר קרא אשת בנך היא משום אשת בנך אתה מחייבו ואי אתה מחייבו משום אשת בנה

just as his daughter-in-law is forbidden him, so is his wife's daughter-in-law forbidden him?<span class="x" onmousemove="('comment',' I.e., the wife of her son by a previous husband. But this is not so. ');">⁵</span>

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