Jerusalem Talmud Yevamot 13.12

משנה: פִּיקַּחַת וְחֵרֶשֶׁת בָּא הַיָּבָם עַל הַפִּיקַּחַת וְחָזַר וּבָא עַל הַחֵרֶשֶׁת. אוֹ שֶׁבָּא אָחִיו עַל הַחֵרֶשֶׁת לֹא פָסַל אֶת הַפִּיקַּחַת. בָּא הַיָּבָם עַל הַחֵרֶשֶׁת וְחָזַר וּבָא עַל הַפִּיקַּחַת אוֹ שֶׁבָּא אָחִיו עַל הַפִּיקַּחַת פָּסַל אֶת הַחֵרֶשֶׁת.

MISHNAH: A hearing wife and a deaf-mute. If the levir had intercourse with the hearing woman and then had intercourse with the deaf-mute, or his brother had intercourse with the deaf-mute, the hearing woman was not disabled. If the levir had intercourse with the deaf-mute and then had intercourse with the hearing woman, or his brother had intercourse with the hearing woman, the deaf-mute was disabled.

הלכה: פִּיקַּחַת וְחֵרֶשֶׁת. בָּא הַיָּבָם כול׳. אֲפִילוּ לֹא בָא עַל הַפִּיקַּחַת פּוֹסֵל אֶת הַחֵרֶשֶׁת. שֶׁאִילּוּ לֹא בָא עַל הַפִּיקַּחַת וָמֵתָה הָיָה מוּתָּר בַּחֵרֶשֶׁת. וְעַכְשָׁיו שֶׁבָּא עָלֶיהָ אֲפִילוּ מֵתָה פָּסַל אֶת הַחֵרֶשֶׁת.

HALAKHAH: “A hearing wife and a deaf-mute. If the levir had intercourse,” etc. Even if he did not have intercourse with the hearing woman, the deaf-mute is disabled. If he did not have intercourse with the hearing woman and she died, he would have been permitted the deaf-mute. But now that he did have intercourse with her, even if she died he had disabled the deaf-mute.