Mishnayos Yevamos Perek 6 Mishnah 5

A common priest may not marry a sexually underdeveloped woman [aylonit], who is incapable of bearing children, unless he already has a wife and children. Rabbi Yehuda says: Even if he has a wife and children, he may not marry a sexually underdeveloped woman, as she is the zona about whom it is stated in the Torah that a priest may not marry her. Intercourse with her is considered a licentious act because she is incapable of bearing children. And the Rabbis say: The only women in the category of zona, who are therefore forbidden to a priest, are a female convert, a freed maidservant, and any woman who engaged in licentious sexual intercourse with a man she is prohibited from marrying.

כֹּהֵן הֶדְיוֹט לֹא יִשָּׂא אַיְלוֹנִית, אֶלָּא אִם כֵּן יֶשׁ לוֹ אִשָּׁה וּבָנִים. רַבִּי יְהוּדָה אוֹמֵר, אַף עַל פִּי שֶׁיֶּשׁ לוֹ אִשָּׁה וּבָנִים, לֹא יִשָּׂא אַיְלוֹנִית, שֶׁהִיא זוֹנָה הָאֲמוּרָה בַתּוֹרָה. וַחֲכָמִים אוֹמְרִים, אֵין זוֹנָה אֶלָּא גִיּוֹרֶת וּמְשֻׁחְרֶרֶת וְשֶׁנִּבְעֲלָה בְעִילַת זְנוּת: