שְׁנַּיִם מִן הָאַחִין נְשׂוּאִין לִשְׁתֵּי אֲחָיוֹת וּמֵתוּ שְׁנֵיהֶם וְלֹא נוֹדַע אֵי זֶה מֵהֶם מֵת רִאשׁוֹן. הוֹאִיל וְאִי אֶפְשָׁר לְיַבֵּם שְׁתֵּיהֶן וַהֲרֵי זִקָּה נָפְלָה עַל שְׁתֵּיהֶן שְׁתֵּיהֶן חוֹלְצוֹת וְלֹא מִתְיַבְּמוֹת. וַאֲפִלּוּ הָיְתָה אַחַת מֵהֶן אֲסוּרָה עַל הַיָּבָם מִשּׁוּם שְׁנִיָּה אוֹ מֵחַיָּבֵי עֲשֵׂה אוֹ מֵחַיָּבֵי לָאוִין הֲרֵי אֵלּוּ חוֹלְצוֹת וְלֹא מִתְיַבְּמוֹת. אֲבָל אִם הָיְתָה אַחַת מֵהֶן עֶרְוָה עָלָיו כְּגוֹן שֶׁהָיְתָה אֵם אִשְׁתּוֹ אוֹ בִּתָּהּ. הֲרֵי אֲחוֹתָהּ מֻתֶּרֶת לוֹ וְרָצָה חוֹלֵץ רָצָה מְיַבֵּם. שֶׁהֲרֵי לֹא נָפְלָה זִקָּתוֹ עַל שְׁתֵּיהֶן, שֶׁאֵין זִקָּה עַל הָעֶרְוָה:
When two brothers were married to two sisters, [the brothers] both died, and it is impossible to know who died first, [a third brother who remains alive] may not perform yibbum with both of them. Since they are both obligated to him, they both must perform chalitzah and not yibbum. [The above ruling applies even] when one [of the yevamot] was forbidden to the yavam as a sh'niyah, or because of a positive commandment or a negative commandment. If, however, one [of the yevamot] was forbidden to the yavam as an ervah - e.g., she was his wife's mother or daughter - the sister is permitted [to the yavam]; he may perform either yibbum or chalitzah, as he desires. For both of the sisters were not obligated to him, since an ervah is not bound by this obligation.
