Reference for Gittin 8:9
הַמְגָרֵשׁ אֶת אִשְׁתּוֹ וְלָנָה עִמּוֹ בְּפֻנְדְּקִי, בֵּית שַׁמַּאי אוֹמְרִים, אֵינָהּ צְרִיכָהּ הֵימֶנּוּ גֵט שֵׁנִי. וּבֵית הִלֵּל אוֹמְרִים, צְרִיכָה הֵימֶנּוּ גֵט שֵׁנִי. אֵימָתַי, בִּזְמַן שֶׁנִּתְגָּרְשָׁה מִן הַנִּשּׂוּאִין. וּמוֹדִים בְּנִתְגָּרְשָׁה מִן הָאֵרוּסִין שֶׁאֵינָהּ צְרִיכָה הֵימֶנּוּ גֵט שֵׁנִי, מִפְּנֵי שֶׁאֵין לִבּוֹ גַס בָּהּ. כְּנָסָהּ בְּגֵט קֵרֵחַ, תֵּצֵא מִזֶּה וּמִזֶּה, וְכָל הַדְּרָכִים הָאֵלּוּ בָהּ:
If one divorced his wife, and she spent the night with him at an inn, [there being witnesses to their having been alone together, but not to their having cohabited], Beth Shammai say: She does not require a second get from him. Beth Hillel say: She requires a second get from him. [Beth Hillel hold that witnesses to their being alone together are (considered) witnesses to cohabitation. And since a man does not cohabit promiscuously, (we assume that) he betrothed her with this cohabitation. And Beth Shammai hold that we do not consider witnesses to their being alone witnesses to cohabitation until they actually observe her in the act.] When is this so? If she were divorced from marriage. They agree that if she were divorced from betrothal, she does not require a second get from him, for he is not that familiar with her (and is assumed not to have cohabited with her.) If one wed her with a "bald get," she leaves this one and this one, and all of the above applies. [A "bald get" is one whose folds are more numerous than its witnesses. The rabbis instituted a folded get (get mekushar) for Cohanim, who are quick to anger and who, in the heat of their anger, might write a get to their wives, and later regret it and not be able to take them back. They, therefore, instituted a get mekushar, which is difficult to write quickly, so that in the interim, their anger might cool. One or two lines are written and folded over on the smooth (unwritten) part and sewn, and one witness signs the fold on the outside. The process is repeated a second and third time. And if there is a fold without a witness signed on the outside, this is a "bald get," and it is not valid. For we assume that in the beginning there were as many witnesses as there are folds, and we suspect that the husband told all of them to sign and that one did not. If she weds with such a get, she leaves both, and all of the above applies. This Mishnah is in accordance with R. Meir, who says: "If one alters 'the currency minted by the sages' for gittin, the child is a mamzer." This is not the halachah.]