Mishnayos Yevamos Perek 8 Mishnah 5

A sexually underdeveloped man does not perform ḥalitza or enter into levirate marriage with his yevama. And similarly, a sexually underdeveloped woman [aylonit], who is incapable of bearing children, does not perform ḥalitza or enter into levirate marriage with her yavam. If a sexually underdeveloped man performed ḥalitza with his yevama, he has not thereby disqualified her from marrying into the priesthood, as his ḥalitza is invalid. However, if he had intercourse with her, he has disqualified her. This is because it is considered licentious sexual intercourse, since such intercourse does not fulfill the mitzva of levirate marriage and is therefore categorized as forbidden relations with one’s sister-in-law. And similarly, with regard to a sexually underdeveloped woman, if one of the brothers performed ḥalitza with her he has not thereby disqualified her from marrying into the priesthood. However, if he had intercourse with her, he has disqualified her because the intercourse is considered licentious sexual intercourse.

הַסָּרִיס לֹא חוֹלֵץ וְלֹא מְיַבֵּם. וְכֵן אַיְלוֹנִית לֹא חוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת. הַסָּרִיס שֶׁחָלַץ לִיבִמְתּוֹ, לֹא פְסָלָהּ. בְּעָלָהּ, פְּסָלָהּ, מִפְּנֵי שֶׁהִיא בְעִילַת זְנוּת. וְכֵן אַיְלוֹנִית שֶׁחָלְצוּ לָהּ אַחִין, לֹא פְסָלוּהָ. בְּעָלוּהָ, פְּסָלוּהָ, מִפְּנֵי שֶׁבְּעִילָתָהּ בְּעִילַת זְנוּת: