Talmud for Yevamot 3:5
שְׁלֹשָׁה אַחִין, שְׁנַיִם מֵהֶם נְשׂוּאִים שְׁתֵּי אֲחָיוֹת, וְאֶחָד מֻפְנֶה, מֵת אֶחָד מִבַּעֲלֵי אֲחָיוֹת, וְעָשָׂה בָהּ מֻפְנֶה מַאֲמָר, וְאַחַר כָּךְ מֵת אָחִיו הַשֵּׁנִי, בֵּית שַׁמַּאי אוֹמְרִים, אִשְׁתּוֹ עִמּוֹ, וְהַלָּה תֵצֵא מִשּׁוּם אֲחוֹת אִשָּׁה. וּבֵית הִלֵּל אוֹמְרִים, מוֹצִיא אֶת אִשְׁתּוֹ בְגֵט וּבַחֲלִיצָה, וְאֵשֶׁת אָחִיו בַּחֲלִיצָה. זוֹ הִיא שֶׁאָמְרוּ, אוֹי לוֹ עַל אִשְׁתּוֹ וְאוֹי לוֹ עַל אֵשֶׁת אָחִיו:
If there were three brothers, two of them married to two sisters, and one of them single — if one of the sisters' husbands died, and the single brother made a ma'amar in her, and then the second brother died — Beth Shammai say: His wife remains with him [For Beth Shammai hold that the woman betrothed by ma'amar is regarded as his wife, so that when her sister falls before him afterwards she is not forbidden by reason of "the sister of his linked one"], and the other goes out [even from chalitzah, by reason of "the sister of his wife."] And Beth Hillel say: He must send his wife away by get and by chalitzah, and his brother's wife by chalitzah. [For ma'amar is not sufficient to give her the status of a married woman, and the other is forbidden by reason of "the sister of his linked one." A get is necessary because of the ma'amar, which is partial betrothal, and betrothal is not dissolved without a get. And she also requires chalitzah, for since the ma'amar is not bona fide betrothal, she is still linked to him (for yibum) and requires chalitzah to dissolve that linkage; so that first he gives her a get, and then chalitzah. And this is the halachah.] And this is the instance of which they said (13:7): "Woe to him by reason of his wife, and woe to him by reason of his brother's wife!"