עֶרְוַת אֲחִי אָבִיךָ לֹא תְגַלֵּה – שֶׁלֹּא לָבוֹא עַל אֲחִי הָאָב וּמִן הַדּוֹמֶה שֶׁאֵין הֶפְרֵשׁ בֵּין שֶׁיִּהְיֶה אֲחִי אָבִיו מִן הָאָב אוֹ מִן הָאֵם, בֵּין מִן הַנִּשּׂוּאִין בֵּין מִן הַזְּנוּת, שֶׁנֶּאֱמַר (ויקרא יח יד) עֶרְוַת אֲחִי אָבִיךָ לֹא תְגַלֵּה, וַאֲחִי אָבִיו נִקְרָא מִכָּל מָקוֹם. וְאַף עַל פִּי שֶׁהַבָּא עַל כָּל זָכָר חַיָּב מִשּׁוּם וְאֶת זָכָר לֹא תִשְׁכַּב וְגוֹ', זֶה הַלָּאו הוּא נוֹסָף בְּמִי שֶׁבָּא עַל אֲחִי אָבִיו, וְאִם יִהְיֶה שׁוֹגֵג יִתְחַיֵּב עָלָיו שְׁתֵּי חַטָּאוֹת מִשּׁוּם לָאו דְּבָא עַל הַזָּכָר, וְלָאו דְּבָא עַל אֲחִי אָבִיו, וּכְמוֹ שֶׁאָמַרְנוּ גַּם כֵּן בְּאָבִיו (במצוה קפט). וּבַגְּמָרָא סַנְהֶדְרִין אָמְרוּ זִכְרוֹנָם לִבְרָכָה (נד, א) הַבָּא עַל אֲחִי אָבִיו חַיָּב שְׁתַּיִם לְדִבְרֵי הַכֹּל. The nakedness of the brother of your father you shall not reveal: To not have intercourse with the brother of the father. And it is from what appears that there is no difference whether he is the brother of his father from the father or from the mother, whether he is from marriage or whether from licentiousness; as it is stated (Leviticus 18:14), “The nakedness of the brother of your father you shall not reveal” — and he is called the brother of his father regardless. And even though [a man] who has intercourse with any male is liable on account of “and with a male you shall not lay, etc.,” this negative commandment is in addition [to that] for the one that has intercourse with the brother of his father. And if he was inadvertent, he is liable for two sin-offerings — on account of the negative commandment of the one who has intercourse with the male, and [on account of] the negative commandment of one who has intercourse with the brother of his father — and as we said also with his father (Sefer HaChinukh 189). And in the Gemara Sanhedrin 54a, they, may their memory be blessed, said, [that] one who has intercourse with the brother of his father is liable for two, according to the words of all.
וְנוֹהֵג אִסּוּר זֶה בְּכָל מָקוֹם וּבְכָל זְמַן. וְהָעוֹבֵר עָלֶיהָ וְשָׁכַב עִם אֲחִי אָבִיו שְׁנֵיהֶם נִסְקָלִים, הַשּׁוֹכֵב וְהַנִּשְׁכָּב, אִם שְׁנֵיהֶם מְזִידִין וּבְעֵדִים וְהַתְרָאָה, וְאִם אֵין עֵדִים שְׁנֵיהֶם בְּכָרֵת, וּבְשׁוֹגֵג חַיָּב הָאֶחָד שְׁתֵּי חַטָּאוֹת כְּמוֹ שֶׁאָמַרְנוּ, שֶׁהַבָּא עַל אֲחִי אָבִיו שֶׁחַיָּב שְׁתֵּי חַטָּאוֹת, וְהָאֶחָד חַטָּאת אֶחָד. And this prohibition is practiced in all places and at all times. And [in the case of] one who transgresses it and laid with the brother of his father, both of them are stoned — the layer and the one who is lain with — if they are both volitional and [it occurred] with witnesses and a warning; if there are no witnesses, they are both [liable] for excision. And when inadvertent, one is liable for two sin-offerings — as we said, that one who has intercourse with the brother of his father is liable for two sin-offerings — and [the] one [who is lain with] is liable one sin-offering.