יבמות ב׳Yevamot 2

Mishnah 3ג׳

כְּלָל אָמְרוּ בַיְבָמָה. כָּל שֶׁהִיא אִסּוּר עֶרְוָה, לֹא חוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת. אִסּוּרָהּ אִסּוּר מִצְוָה, וְאִסּוּר קְדֻשָּׁה, חוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת. אֲחוֹתָהּ שֶׁהִיא יְבִמְתָּהּ, חוֹלֶצֶת אוֹ מִתְיַבֶּמֶת:

A general principle was stated in respect to a yevamah: If she is an issur ervah (interdicted as an ervah), she [her tzarah, and, it goes without saying, she herself], is subject to neither chalitzah nor yibum. [The same applies to an eilonith, it being written (Deuteronomy 25:6): "And it shall be, the first-born that she bears" — to exclude an eilonith. Likewise, the wife of a seris chammah (one born without testicles), and a hermaphrodite is subject to neither chalitzah not yibum, it being written (Ibid. 5): "and he have no son" — to exclude those who are incapable of begetting children. And the wife of a proselyte and of a freed bondsman is subject to neither chalitzah not yibum, there being no "brotherhood" to proselytes nor bondsmen. But a barren woman or an old woman receive chalitzah or are taken in yibum.] If she were interdicted as issur mitzvah or issur kedushah (see next Mishnah), she is subject to chalitzah, but not to yibum. If her sister [the sister of an ervah] were her yevamah [as when two sisters from his two brothers fell before him for yibum, one of them being forbidden to him as an ervah (e.g., his mother-in-law or his daughter-in-law)], she either receives chalitzah or is taken in yibum [For in such an instance, he is not in contravention of "the sister of one linked to him (in yibum)," an ervah not being linked to him].

Mishnah 4ד׳

אִסּוּר מִצְוָה, שְׁנִיּוֹת מִדִּבְרֵי סוֹפְרִים. אִסּוּר קְדֻשָּׁה, אַלְמָנָה לְכֹהֵן גָּדוֹל, גְּרוּשָׁה וַחֲלוּצָה לְכֹהֵן הֶדְיוֹט, מַמְזֶרֶת וּנְתִינָה לְיִשְׂרָאֵל, וּבַת יִשְׂרָאֵל לְנָתִין וּמַמְזֵר:

Issur mitzvah — shniyoth [secondary to arayoth] interdicted by the soferim. [They are called "issur mitzvah" because it is a mitzvah to hearken to the words of the sages. The shniyoth are: the mother of his mother (all the way down the line), the mother of his father's mother alone, the mother of his father (all the way down the line), the mother of his father's father, the wife of his father's father (all the way down the line), the wife of his father's mother (alone), the wife of his father's brother from the mother, the wife of his mother's brother, whether from the mother or from the father, the daughter-in-law of his son (all the way down the line), the daughter-in-law of his daughter, the daughter of the daughter of his son, the daughter of the daughter of his daughter, the daughter of the son of his son, the daughter of the son of his daughter, the daughter of the daughter of the son of his wife, the daughter of the daughter of the daughter of his wife, the mother of the mother of the father of his wife, the mother of the mother of the mother of his wife, the mother of the father of the mother of his wife, and the mother of the father of the father of his wife.] Issur kedushah — a widow to a high-priest [in an instance where his brother, a Cohein, died, and his wife fell before him (for yibum)], a divorced woman and a chalutzah to a plain Cohein [as when his dead brother had transgressed and married a divorced woman or a chalutzah. When he dies, she requires chalitzah, for betrothal "takes" in her (betrothal) "taking" in those interdicted by negative commandment (but not subject to kareth). But he does not take her in yibum, for she is forbidden to him. And simply to exempt her is impossible, the negative commandment not sufficing to exempt her, our deriving this (exemption) from the (instance of the) sister of one's wife, where kareth obtains], a mamzereth and a Nethinah to a Yisrael, and the daughter of a Yisrael to a Nathin and to a mamzer.