Reference for Bava Batra 269:1

ההוא דהוה קא שכיב אמרו ליה אתתיה למאן אמר להו חזיא לכהנא רבה

[Once] a certain [man] was dying.<span class="x" onmousemove="('comment',' Who had brothers but no sons. ');">¹</span> Being asked to whom his wife [was permitted to be married<span class="x" onmousemove="('comment',' I.e., whether she was subject to the laws of levirate marriage. ');">²</span>

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