יבמות ח׳Yevamot 8

Mishnah 3ג׳

עַמּוֹנִי וּמוֹאָבִי, אֲסוּרִים, וְאִסּוּרָן אִסּוּר עוֹלָם, אֲבָל נְקֵבוֹתֵיהֶם מֻתָּרוֹת מִיָּד. מִצְרִי וַאֲדוֹמִי אֵינָם אֲסוּרִים אֶלָּא עַד שְׁלֹשָׁה דוֹרוֹת, אֶחָד זְכָרִים וְאֶחָד נְקֵבוֹת. רַבִּי שִׁמְעוֹן מַתִּיר אֶת הַנְּקֵבוֹת מִיָּד. אָמַר רַבִּי שִׁמְעוֹן, קַל וָחֹמֶר הַדְּבָרִים, וּמָה אִם בִּמְקוֹם שֶׁאָסַר אֶת הַזְּכָרִים אִסּוּר עוֹלָם, הִתִּיר אֶת הַנְּקֵבוֹת מִיָּד, מְקוֹם שֶׁלֹּא אָסַר אֶת הַזְּכָרִים אֶלָּא עַד שְׁלֹשָׁה דוֹרוֹת, אֵינוֹ דִין שֶׁנַּתִּיר אֶת הַנְּקֵבוֹת מִיָּד. אָמְרוּ לוֹ, אִם הֲלָכָה נְקַבֵּל, וְאִם לַדִּין, יֵשׁ תְּשׁוּבָה. אָמַר לָהֶם, לֹא כִי, הֲלָכָה אֲנִי אוֹמֵר. מַמְזֵרִין וּנְתִינִין, אֲסוּרִין, וְאִסּוּרָן אִסּוּר עוֹלָם, אֶחָד זְכָרִים, וְאֶחָד נְקֵבוֹת:

An Ammonite and a Moabite are forbidden [to enter into the congregation of Israel] and their prohibition is forever. However, their women are permitted immediately [following conversion]. Both male and female Egyptians and Edomites are forbidden only until the third generation. Rabbi Shimon permits their women immediately. Said Rabbi Shimon: This follows a fortiori reasoning: If in a case where males are forbidden forever the females are [nevertheless] permitted immediately [upon conversion], then in a case where males are forbidden only until the third generation how much more so should females be permitted immediately [upon conversion]. They [the Sages] said to him: If this is a received tradition we shall accept it, but if it is only a logical inference there is a refutation. He replied: No! I am in fact reporting a received tradition. Mamzerim [a Mamzer is the offspring of a severely prohibited union between a Jewish man and woman] and Netinim [a Netin is a member of a caste of Temple servants historically descended from the Gibeonites] are forbidden [from marrying into the nation] and their prohibition is forever. [This restriction bans] both males and females.

Mishnah 4ד׳

אָמַר רַבִּי יְהוֹשֻׁעַ, שָׁמַעְתִּי שֶׁהַסָּרִיס חוֹלֵץ, וְחוֹלְצִין לְאִשְׁתּוֹ, וְהַסָּרִיס לֹא חוֹלֵץ וְלֹא חוֹלְצִין לְאִשְׁתּוֹ, וְאֵין לִי לְפָרֵשׁ. אָמַר רַבִּי עֲקִיבָא, אֲנִי אֲפָרֵשׁ. סְרִיס אָדָם חוֹלֵץ וְחוֹלְצִין לְאִשְׁתּוֹ, מִפְּנֵי שֶׁהָיְתָה לוֹ שְׁעַת הַכֹּשֶׁר. סְרִיס חַמָּה לֹא חוֹלֵץ וְלֹא חוֹלְצִין לְאִשְׁתּוֹ, מִפְּנֵי שֶׁלֹּא הָיְתָה לוֹ שְׁעַת הַכֹּשֶׁר. רַבִּי אֶלְעָזָר אוֹמֵר, לֹא כִי, אֶלָּא סְרִיס חַמָּה חוֹלֵץ, וְחוֹלְצִין לְאִשְׁתּוֹ, מִפְּנֵי שֶׁיֶּשׁ לוֹ רְפוּאָה. סְרִיס אָדָם לֹא חוֹלֵץ וְלֹא חוֹלְצִין לְאִשְׁתּוֹ, מִפְּנֵי שֶׁאֵין לוֹ רְפוּאָה. הֵעִיד רַבִּי יְהוֹשֻׁעַ בֶּן בְּתֵירָא עַל בֶּן מְגוּסַת שֶׁהָיָה בִירוּשָׁלַיִם סְרִיס אָדָם, וְיִבְּמוּ אֶת אִשְׁתּוֹ, לְקַיֵּם דִּבְרֵי רַבִּי עֲקִיבָא:

Rabbi Yehoshua said: I have heard that a eunuch undergoes Chalitzah [the ceremony releasing the widow of a childless man from the obligation of Levirate marriage] and that one undergoes Chalitzah for his wife; and that a eunuch does not undergo Chalitzah and that one does not undergo Chalitzah for his wife, but I am unable to explain this. Rabbi Akiva said: I will explain it: a man-eunuch [castrated by a person] undergoes Chalitzah and one undergoes Chalitzah for his wife because there was a time when he was fit [to have children]; a sun-eunuch [who was born that way] does not undergo Chalitzah nor does one undergo Chalitzah for his wife since there was never a time when he was fit. Rabbi Eliezer says: Not so! Rather, a sun-eunuch undergoes Chalitzah and one undergoes Chalitzah for his wife because because there is a cure; a man-eunuch does not undergo Chalitzah nor does one undergo Chalitzah for his wife since he has no cure. Rabbi Yehoshua ben Betiera testified concerning Ben Megusat who was a man-eunuch in Jerusalem and they performed Yibum [Levirate marriage wherein a man weds his childless brother's widow] for his wife, to uphold the opinion of Rabbi Akiva.