Mishnayos Yevamos Perek 13 Mishnah 11

If the deceased brother had two wives, an adult and a minor, and the yavam engaged in sexual intercourse with the adult, then engaged in intercourse with the minor, or if his brother engaged in intercourse with the minor, the yavam or his brother did not disqualify the adult from staying married, as the consummation of the levirate marriage with the adult completely dissolves the levirate bond. If the yavam engaged in intercourse with the minor, and then engaged in intercourse with the adult, or if his brother engaged in intercourse with the adult, the yavam or his brother disqualified the minor from staying married. Rabbi Elazar says: The court instructs the minor to refuse him thereby annulling her marriage retroactively, and then the minor is permitted to marry any man.

גְּדוֹלָה וּקְטַנָּה, בָּא יָבָם עַל הַגְּדוֹלָה, וְחָזַר וּבָא עַל הַקְּטַנָּה, אוֹ שֶׁבָּא אָחִיו עַל הַקְּטַנָּה, לֹא פָסַל אֶת הַגְּדוֹלָה. בָּא יָבָם עַל הַקְּטַנָּה, וְחָזַר וּבָא עַל הַגְּדוֹלָה, אוֹ שֶׁבָּא אָחִיו עַל הַגְּדוֹלָה, פָּסַל אֶת הַקְּטַנָּה. רַבִּי אֶלְעָזָר אוֹמֵר, מְלַמְּדִין הַקְּטַנָּה שֶׁתְּמָאֵן בּוֹ: