Mishnayos Yevamos Perek 4 Mishnah 9

In the case of a widow waiting for her yavam to consummate levirate marriage or perform ḥalitza with her, and the brother of the yavam betrothed her sister, they said in the name of Rabbi Yehuda ben Beteira: They say to the brother: Wait and do not marry the woman you betrothed until your brother performs an act, either of ḥalitza or of consummating the levirate marriage, as until he does there remains a levirate bond between the yevama and each of the brothers, and it is prohibited to marry the sister of a woman to whom one is bound by a levirate bond. If a brother of the one who betrothed the sister of the yevama performed ḥalitza with the yevama or consummated a levirate marriage with her, since by doing so the levirate bond between the yevama and the one who betrothed her sister is dissolved, he may then enter into marriage with his wife, who until that point was only betrothed to him, as she is no longer the sister of a woman to whom he is bound by a levirate bond. Similarly, if the yevama died, since his levirate bond to her is dissolved upon her death, he may proceed to enter into marriage with his betrothed wife. However, if the yavam died without performing an act that would have dissolved the levirate bond, he must divorce his wife with a bill of divorce, as she is forbidden to him as the sister of a woman to whom he is bound by a levirate bond, and his brother’s wife he must send out with ḥalitza, as she is forbidden to him as the sister of his divorcée.

שׁוֹמֶרֶת יָבָם שֶׁקִּדֵּשׁ אָחִיו אֶת אֲחוֹתָהּ, מִשּׁוּם רַבִּי יְהוּדָה בֶן בְּתֵירָא אָמְרוּ, אוֹמְרִים לוֹ, הַמְתֵּן עַד שֶׁיַּעֲשֶׂה אָחִיךָ הַגָּדוֹל מַעֲשֶׂה. חָלַץ לָהּ אָחִיו, אוֹ כְנָסָהּ, יִכְנֹס אֶת אִשְׁתּוֹ. מֵתָה הַיְּבָמָה, יִכְנֹס אֶת אִשְׁתּוֹ. מֵת יָבָם, יוֹצִיא אֶת אִשְׁתּוֹ בְגֵט, וְאֵשֶׁת אָחִיו בַּחֲלִיצָה: