Jerusalem Talmud Yevamot 2.10

משנה: מִצְוָה בַגָּדוֹל לְיַיבֶּם וְאִם קָדַם הַקָּטָן זָכָה. הַנִּטְעָן עַל הַשִּׁפְחָה וְנִשְׁתַּחְרְרָה אוֹ עַל הַנָּכְרִית וְנִתְגַּיְירָה הֲרֵי זֶה לֹא יִכְנוֹס וְאִם כָּנַס אֵין מוֹצִיאִין מִיָּדוֹ. הַנִּטְעָן עַל אֵשֶׁת אִישׁ וְהוֹצִיאוּהָ מִתַּחַת יָדוֹ אַף עַל פִּי שֶׁכָּנַס יוֹצִיא.

MISHNAH: The obligation of levirate is on the oldest [brother] but if a younger one got the start on him, he acquired. If somebody is accused in matters of a slave woman and she was manumitted, or of a Gentile and she converted, he should not marry her but if he married her one does not remove her from him. If somebody is accused in matters of a married woman and she was forcibly divorced from [her husband], even if he married her he must divorce her.

הלכה: מִצְוָה בַגָּדוֹל לְיַיבֶּם וְאִם קָדַם הַקָּטָן זָכָה כול׳. מִצְוָה בַגָּדוֹל לְיַיבֶּם. שֶׁנֶּאֱמָר וְהָיָה הַבְּכוֹר אֲשֶׁר תֵּלֵד. מַה אֲנָן קַיָימִין. אִם בְּנוֹלָד. יֹאמַר קִרְיָיא יָקוּם עַל שֵׁם אָבִיו הַמֵּת. אֶלָּא עַד שֶׁיְּהֵא הַנּוֹלָד בְּכוֹר. מֵעַתָּה אֲפִילוּ הָיוּ לוֹ בָנִים וּמֵתוּ וְאַחַר כָּךְ מֵת הוּא לֹא תִהְיֶה אִשְׁתּוֹ זְקוּקָה לְיִיבּוּם. וְיֹאמַר קִרְיָיה וּבָנִים לֹא הָיוּ לוֹ. אֶלָּא אִם אֵינוֹ עִנְיָין לַנּוֹלָד תְּנֵיהוּ עִנְיָין לַמְיַיבֶּם. מִצְוָה בַגָּדוֹל לְיַיבֶּם.

HALAKHAH: “The obligation of levirate is on the oldest [brother] but if a younger one got the start on him, he acquired, etc.” “The obligation of levirate is on the oldest,” since it is said, “the firstborn she will bear shall …”. How do we hold? If about the newborn, the verse should read “he should rise in the name of his dead father.” But it must be that the newborn is a firstborn. In that case, even if he had children and they died before he died, his widow should not be a candidate for levirate! Then the verse should have said, “he never had children”. But if it cannot refer to the newborn; let it refer to the levir, “the obligation of levirate is on the oldest.”

הַנִּטְעָן עַל הַשִּׁפְחָה וְנִשְׁתַּחְרְרָה אוֹ עַל הַנָּכְרִית וְנִתְגַּיְירָה הֲרֵי זֶה לֹא יִכְנוֹס. קִידֵּשׁ כְּמִי שֶׁכָּנַס. אָמַר [מִדִּין] שֶׁלֹּא לִכְנוֹס וְכָנַס מוֹצִיאוֹ מִיָּדוֹ. גֵּירַשׁ מַהוּ שֶׁיַּחֲזִיר. אִם אוֹמֵר אַתְּ כֵּן לֹא נִמְצֵאת מוֹצִיא לִיזָה עַל בָּנֶיהָ. הַנִּטְעָן עַל אֵשֶׁת אִישׁ. רַב אָמַר בְּנִטְעָן בְּעֵדִים. רִבִּי יוֹסֵי בָּעֵי. אִם בְּנִטְעָן בְּעֵדִים בְּהָא תַנֵּי [וְהוֹצִיאָהּ] מִתַּחַת יָדוֹ. אַף עַל פִּי שֶׁכָּנַס יוֹצִיא. וּמִתַּחַת יְדֵי אַחֵר יְקַיֵים. אִם נִטְעָן בְּעֵדִים אֲפִילוּ מִתַּחַת יְדֵי אַחֵר יוֹצִיא. אֶלָּא כֵּן אֲנָן קַיָימִין בְּנִטְעָן שֶׁלֹּא בְעֵדִים [וְהוֹצִיאָהּ] מִתַּחַת יְדֵי אַחֵר יְקַיֵים.

“If somebody is accused in matters of a slave woman and she was manumitted, or of a Gentile and she converted, he should not marry her but if he married her one does not remove her from him.” If he agreed lawfully not to marry her and [nevertheless] married her, she is forcibly removed from him. If he divorced her, may he take her back? If you would say that, would you not defame her children? “If somebody is accused in matters of a married woman,” Rav said, that is, he was accused by witnesses. Rebbi Yose asked, if he was accused by witnesses, is that what was stated: If he divorced her, even if he married her, he must divorce her? If somebody else divorced her, he can keep her! If he was accused by witnesses, even if somebody else divorced her, he must divorce her! But that is what we deal with: If he was accused not by witnesses, if somebody else divorced her, he may keep her.