10הָיְתָה הַיְבָמָה אֲסוּרָה עַל יְבָמָהּ אִסּוּר לָאו אוֹ אִסּוּר עֲשֵׂה אוֹ שֶׁהָיְתָה שְׁנִיָּה הֲרֵי זוֹ חוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת. וּמִפְּנֵי מָה צְרִיכָה חֲלִיצָה מִפְּנֵי שֶׁיֵּשׁ בָּהּ לִקּוּחִין הוֹאִיל וְקִדּוּשִׁין תּוֹפְסִין בָּהֶן הֲרֵי הֵן זְקוּקוֹת לְיָבָם. וּמִן הַדִּין הָיָה שֶׁיִּתְיַבְּמוּ שֶׁהַיִּבּוּם מִצְוַת עֲשֵׂה וְכָל מָקוֹם שֶׁאַתָּה מוֹצֵא עֲשֵׂה וְלֹא תַּעֲשֶׂה יָבֹא עֲשֵׂה וְיִדְחֶה אֶת לֹא תַּעֲשֶׂה. אֲבָל חֲכָמִים גָּזְרוּ שֶׁלֹּא יִתְיַבְּמוּ חַיָּבֵי לָאוִין וְלֹא שְׁנִיּוֹת גְּזֵרָה שֶׁמָּא יָבוֹא עָלֶיהָ פַּעַם שְׁנִיָּה וַהֲרֵי בִּיאָתָהּ אֲסוּרָה וְאֵין שָׁם מִצְוָה שֶׁאֵין מִצְוַת עֲשֵׂה אֶלָּא בִּיאָה רִאשׁוֹנָה בִּלְבַד. לְפִיכָךְ אִם עָבַר וּבָעַל יְבִמְתּוֹ הָאֲסוּרָה לוֹ מִשּׁוּם לָאו אוֹ מִשּׁוּם עֲשֵׂה וְאֵין צָרִיךְ לוֹמַר שְׁנִיָּה הֲרֵי זֶה קָנָה קִנְיָן גָּמוּר וּמוֹצִיאָהּ בְּגֵט וְהִיא וְכָל צָרוֹתֶיהָ מֻתָּרוֹת לְזָר שֶׁהֲרֵי נִפְטְרוּ:
If the yevamah was forbidden to her yavam because of a negative commandment or a positive commandment, or she was one of the sh'niyot, she should perform chalitzah, but not yibbum. Why is she obligated to perform chalitzah? Because she is fit to be married, and her consecration [by the yavam] would be binding. Therefore, she is under obligation to the yavam. And according to law, she should perform yibbum, for yibbum is a positive commandment, and whenever the observance of a positive commandment conflicts with the observance of a negative commandment, the positive commandment takes precedence. Nevertheless, our Sages decreed that neither woman with whom relations are prohibited by a negative commandment, nor sh'niyot should perform yibbum, lest [the yavam] engage in relations with her a second time. [At that time,] relations with her are forbidden, and there is no mitzvah, for the positive commandment [of yibbum] applies only with regard to the first time [the couple] engage in relations. Therefore, if [the yavam] transgresses and engages in relations with a yevamah who is forbidden to him because of a negative commandment or because of a positive commandment, he acquires her [as his wife] in definitive manner and must divorce her with a get. Needless to say, [this ruling applies] with regard to a sh'niyah. [After the divorce, the yevamah] and all the other wives [of the deceased] are permitted to marry other men, for they have been released of their obligation.