Reference for Gittin 8:8
כָּתַב סוֹפֵר גֵּט לָאִישׁ וְשׁוֹבֵר לָאִשָּׁה, וְטָעָה וְנָתַן גֵּט לָאִשָּׁה וְשׁוֹבֵר לָאִישׁ, וְנָתְנוּ זֶה לָזֶה, וּלְאַחַר זְמַן הֲרֵי הַגֵּט יוֹצֵא מִיַּד הָאִישׁ, וְשׁוֹבֵר מִיַּד הָאִשָּׁה, תֵּצֵא מִזֶּה וּמִזֶּה, וְכָל הַדְּרָכִים הָאֵלּוּ בָהּ. רַבִּי אֱלִיעֶזֶר אוֹמֵר, אִם לְאַלְתַּר יָצָא, אֵין זֶה גֵט. אִם לְאַחַר זְמַן יָצָא, הֲרֵי זֶה גֵט. לֹא כָל הֵימֶנּוּ מִן הָרִאשׁוֹן לְאַבֵּד זְכוּתוֹ שֶׁל שֵׁנִי. כָּתַב לְגָרֵשׁ אֶת אִשְׁתּוֹ וְנִמְלַךְ, בֵּית שַׁמַּאי אוֹמְרִים, פְּסָלָהּ מִן הַכְּהֻנָּה. וּבֵית הִלֵּל אוֹמְרִים, אַף עַל פִּי שֶׁנְּתָנוֹ לָהּ עַל תְּנַאי וְלֹא נַעֲשָׂה הַתְּנַאי, לֹא פְסָלָהּ מִן הַכְּהֻנָּה:
If the scribe wrote a get for the man [to divorce his wife with], and a receipt for the woman [to give to her husband upon payment of her kethubah], and he [the scribe] erred [when he gave them the writs] and gave the get to the woman and the receipt to the man, and they gave it, one to the other, [and she went and married, thinking that what her husband gave her was the get, and he thinking that what his wife gave him was the receipt (Rambam reads it: "And he gave the get to the man and the receipt to the woman," and interprets it as: "And he thought he gave the get to the man and the receipt to the woman," not having done this, but the very opposite. The interpretation is forced.] — and, subsequently, the get was found to issue from the hand of the man, and the receipt from the hand of the woman, she leaves this one and this one, and all of the above applies. R. Eliezer says: If it issued forth at once [from her husband's hand before she remarried], it is not a get, [and she requires a different get], and if it issued forth after some time, [i.e., after she remarried], it is a get. It is not entirely up to him [i.e., It is not all according to the words of the first (husband), that he be believed] to void the rights of the second, [who married her, and we posit a "conspiracy" between the two, an exchange of the writs after she remarried. The halachah is in accordance with R. Eliezer.] If one wrote (a get) to divorce his wife, and changed his mind — Beth Shammai say: He disqualifies her from (marriage to) the priesthood. Beth Hillel say: Even if he gave it to her on condition, and the condition was not satisfied, he does not disqualify her from the priesthood.