אבן העזר קמ״טEven HaEzer 149

Se’if 1א׳

הַמְגָרֵשׁ אֶת אִשְׁתּוֹ, וְחָזַר וּבְעָלָהּ בִּפְנֵי עֵדִים, אוֹ שֶׁגָּלוּי לַכֹּל שֶׁבָּא עָלֶיהָ, כְּגוֹן שֶׁנְשָׂאָהּ (הָרַ"ן פֶּרֶק כָּל הַגֵּט), קֹדֶם שֶׁתִּנָּשֵׂא לְאַחֵר, בֵּין שֶׁגֵּרְשָׁהּ מִן הַנִּשּׂוּאִין בֵּין מִן הָאֵרוּסִין, הוֹאִיל וְאִשְׁתּוֹ הָיְתָה, הֲרֵי זוֹ בְּחֶזְקַת שֶׁהֶחֱזִירָהּ וּלְשֵׁם קִדּוּשִׁין בָּעַל וְלֹא לְשֵׁם זְנוּת. וַאֲפִלּוּ רָאוּ שֶׁנָּתַן לָהּ מָעוֹת, שֶׁחֲזָקָה הִיא שֶׁאֵין אָדָם עוֹשֶׂה בְּעִילָתוֹ בְּעִילַת זְנוּת וַהֲרֵי בְּיָדוֹ לַעֲשׂוֹתָהּ בְּעִילַת מִצְוָה. לְפִיכָךְ, הֲרֵי זוֹ מְקֻדֶּשֶׁת קִדּוּשֵׁי וַדַּאי, וּצְרִיכָה מִמֶּנּוּ גֵּט שֵׁנִי:

If one divorces his wife, and then engages in sexual relations with her before witnesses --italics: or it is evident to everyone that he engaged in sexual relations with her, like he married her (the Ran in the chapter titled "Every Get"-- before she married another, whether he divorced her from betrothal or marriage, since she was his wife, we assume that he took her back [as his wife] and for the sake of marriage he engaged in relations [with her] and not for prostitution. And even if they saw that he gave her money, for there is an assumption that a person doesn't engage in sexual relations for prostitution, and it's in his capability to make these sexual relations for a commandment [that is, for marriage purposes]. Therefore, this [woman] is definitely married, and requires a second get (that is, divorce document).

Se’if 2ב׳

נִתְיַחֵד עִמָּהּ בִּפְנֵי שְׁנֵי עֵדִים, וְהָיוּ שְׁנֵי עֵדִים כְּאֶחָד, וְרָאוּ הוּא וְהִיא אֶת הָעֵדִים, אִם הָיְתָה מְגֹרֶשֶׁת מִן הַנִּשּׂוּאִין, חוֹשְׁשִׁין לָהּ שֶׁמָּא נִבְעֲלָה, וְהֵן הֵן עֵדֵי יִחוּד הֵן הֵן עֵדֵי בִּיאָה. לְפִיכָךְ, הִיא סָפֵק מְקֻדֶּשֶׁת, וּצְרִיכָה גֵּט מִסָפֵק. וְאִם הָיְתָה מְגֹרֶשֶׁת מִן הָאֵרוּסִין, אֵין חוֹשְׁשִׁין לָהּ, שֶׁהֲרֵי אֵין לִבּוֹ גַּס בָּהּ. וְאִי חָזֵינָן לְהוּ דְּגַיְסֵי אַהֲדָדֵי, חוֹשְׁשִׁין לָהּ. הַגָּה: אֲבָל אִם נִתְיַחֵד עִם מְשֻׁדֶּכֶת שֶׁלּוֹ, אַף עַל גַּב דְּגָס בָּהּ, לֹא חַיְשִׁינָן, אֶלָּא אִם כֵּן בָּא עָלֶיהָ בִּפְנֵי עֵדִים (תְּשׁוּבַת הָרַמְבַּן סִימָן קל"ה):

If he was alone with her before two witnesses, and the two witnesses [testified] as one, and he and she saw the witnesses, if she were divorced from marriage, we are concerned that they had sex, and the witnesses of their being alone are witnesses that they had sex. Therefore, there is doubt as to whether this constitutes a marriage, and she requires a bill of divorce out of uncertainty. If she had been divorced from betrothal, we are not concerned about her, for he does not desire her. If we see that they do desire each other, we are concerned about her. Rem"a: If he was alone with his match, even though he desires her, we are not concerned, unless he had sex with her before witnesses (Responsa of the Ramba"n #135).

Se’if 3ג׳

מִי שֶׁשָּׁלַח גֵּט לְאִשְׁתּוֹ, וְאַחַר כָּךְ בִּטְּלוֹ, וְהָלַךְ וְנִתְיַחֵד עִמָּהּ, וְאַחַר כָּךְ נִתְבָּרֵר שֶׁכְּבָר הִגִּיעַ הַגֵּט לְיָדָהּ קֹדֶם בִּטּוּלוֹ, אֵינָהּ צְרִיכָה מִמֶּנּוּ גֵּט שֵׁנִי, דְּוַדַּאי לֹא בָּעַל לְשֵׁם קִדּוּשִׁין, כִּי הָיָה סָבוּר שֶׁהַגֵּט הָיָה בָּטֵל, וְלֹא בָּעַל אֶלָּא עַל דַּעַת קִדּוּשִׁין הָרִאשׁוֹנִים:

One who sent a bill of divorce, and nullified it afterward, and went and was alone with her, and afterward to became clear that she already received the bill of divorce before his nullification, she does not require a second bill of divorce from him, for he certainly would not have had sex with her for the purposes of betrothal, for he believed that the bill of divorce had been nullified, and he only had sex with her by virtue of the original betrothal.