Reference for Yevamot 26:3

<big><strong>גמ׳</strong></big> אמר רבי שמעון בן פזי מאי טעמא דבית שמאי דכתיב (דברים כה, ה) לא תהיה אשת המת החוצה לאיש זר חוצה מכלל דאיכא פנימית ואמר רחמנא לא תהיה

THOUGH THESE FORBADE WHAT THE OTHERS PERMITTED, AND THESE REGARDED AS INELIGIBLE WHAT THE OTHERS DECLARED ELIGIBLE, BETH SHAMMAI, NEVERTHELESS, DID NOT REFRAIN FROM MARRYING WOMEN FROM [THE FAMILIES OF] BETH HILLEL, NOR DID BETH HILLEL [REFRAIN FROM MARRYING WOMEN] FROM [THE FAMILIES OF] BETH SHAMMAI. [SIMILARLY, IN RESPECT OF] ALL [QUESTIONS OF RITUAL] CLEANNESS AND UNCLEANNESS, WHICH THESE DECLARED CLEAN WHERE THE OTHERS DECLARED UNCLEAN, NEITHER OF THEM ABSTAINED FROM USING THE UTENSILS OF THE OTHERS FOR THE PREPARATION OF FOOD THAT WAS RITUALLY CLEAN.<span class="x" onmousemove="('comment',' Lit., 'do clean things, these upon these'. ');">⁷</span> <b><i>GEMARA</i></b>. R. Simeon b. Pazzi said: What is Beth Shammai's reason?<span class="x" onmousemove="('comment',' For permitting the rivals to marry the other brothers. ');">⁸</span> — Because it is written, The outside<span class="x" onmousemove="('comment',' [H] is rendered, 'the one who is the outside one', the word being regarded as an adjective fem. with the relative. E.V., 'abroad'. ');">⁹</span>

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