Kerisus3: 7
אָמַר רַבִּי עֲקִיבָא: שָׁאַלְתִּי אֶת־ רַבָּן גַּמְלִיאֵל וְאֶת־רַבִּי יְהוֹשֻׁעַ בָּאִטְלִיס שֶׁל־אֶמָּאוֹם שֶׁהָלְכוּ לִקַּח בְּהֵמָה לְמִשְׁתֵּה בְנוֹ שֶׁל־רַבָּן גַּמְלִיאֵל: הַבָּא עַל־אֲחוֹתוֹ, וְעַל־אֲחוֹת אָבִיו, וְעַל־אֲחוֹת אִמּוֹ, בְּהֶעְלֵם אֶחָד — מַהוּ? חַיָּב אַחַת עַל־כֻּלָּן אוֹ אַחַת עַל־כָּל־אַחַת וְאַחַת? וְאָמְרוּ לִי: לֹא שָׁמַעְנוּ, אֲבָל שָׁמַעְנוּ הַבָּא עַל־חֲמֵשׁ נָשָׁיו נִדּוֹת, בְּהֶעְלֵם אֶחָד, שֶׁהוּא חַיָּב עַל־כָּל־אַחַת וְאַחַת, וְרוֹאִין אָנוּ שֶׁהַדְּבָרִים קַל וָחֹמֶר.
Said R’ Akiva: I asked Rabban Gamliel and R’ Yehoshua in the meat market of Emmaus when they went to purchase an animal for Rabban Gamliel’s son’s feast: One who cohabits with his sister, his father’s sister, and his mother’s sister, in one lapse of awareness — what is he [liable for]? Is he liable to one [chatas] for all of them or one for each? And they replied to me: [This] we have not heard, but we have heard that one who cohabits with his five menstruous wives, in a single lapse of awareness, is liable for each one, and we believe that the matter is a kal vachomer.