Mishnayos Yevamos Perek 4 Mishnah 13

Which offspring of forbidden relations have the status of a mamzer? It is the offspring of a union with any next of kin that is subject to a Torah prohibition that he should not engage in sexual relations with them; this is the statement of Rabbi Akiva. Shimon HaTimni says: It is the offspring of a union with any forbidden relation for which one is liable to receive karet at the hand of Heaven. And the halakha is in accordance with his statement. Rabbi Yehoshua says: It is the offspring of a union with any forbidden relation for which one is liable to receive court-imposed capital punishment. Rabbi Shimon ben Azzai said: I found a scroll recording people’s lineages in Jerusalem, and it was written in it that so-and-so is a mamzer from an adulterous union with a married woman, a sin punishable by court-imposed capital punishment. The only reason for the scroll to state the reason that this individual is a mamzer is in order to support the statement of Rabbi Yehoshua. The mishna delineates the circumstances in which it is prohibited to engage in relations with the sister of one’s wife and the sister of one’s yevama: If a man’s wife died, he is permitted to her sister. If he divorced her and then she died, he is permitted to her sister. If he divorced his wife and then she was married to another and then died, he is permitted to her sister. If his yevama died, he is permitted to her sister. If he performed ḥalitza with her and then she died, he is permitted to her sister. If after ḥalitza she was married to another and then died, he is permitted to her sister. The principle underlying all these cases is that the prohibition against engaging in relations with her sister only applies while the wife or yevama remain alive, irrespective of their current relationship to the man.

אֵיזֶהוּ מַמְזֵר, כָּל שְׁאֵר בָּשָׂר שֶׁהוּא בְלֹא יָבֹא דִּבְרֵי רַבִּי עֲקִיבָא. שִׁמְעוֹן הַתִּימְנִי אוֹמֵר, כָּל שֶׁחַיָּבִין עָלָיו כָּרֵת בִּידֵי שָׁמַיִם. וַהֲלָכָה כִדְבָרָיו. רַבִּי יְהוֹשֻׁעַ אוֹמֵר, כָּל שֶׁחַיָּבִים עָלָיו מִיתַת בֵּית דִּין. אָמַר רַבִּי שִׁמְעוֹן בֶּן עַזַּאי, מָצָאתִי מְגִלַּת יֻחֲסִין בִּירוּשָׁלַיִם וְכָתוּב בָּהּ, אִישׁ פְּלוֹנִי מַמְזֵר מֵאֵשֶׁת אִישׁ, לְקַיֵּם דִּבְרֵי רַבִּי יְהוֹשֻׁעַ. אִשְׁתּוֹ שֶׁמֵּתָה, מֻתָּר בַּאֲחוֹתָהּ. גֵּרְשָׁהּ וָמֵתָה, מֻתָּר בַּאֲחוֹתָהּ. נִשֵּׂאת לְאַחֵר וָמֵתָה, מֻתָּר בַּאֲחוֹתָהּ. יְבִמְתּוֹ שֶׁמֵּתָה, מֻתָּר בַּאֲחוֹתָהּ. חָלַץ לָהּ וָמֵתָה, מֻתָּר בַּאֲחוֹתָהּ: