יורה דעה פ״זYoreh De'ah 87

Se’if 1א׳

כָּתוּב בַּתּוֹרָה: לֹא תְבַשֵּׁל גְּדִי בַּחֲלֵב אִמּוֹ (שְׁמוֹת כג, יט, לד, כו, דְּבָרִים יד, כא) ג' פְּעָמִים; אֶחָד לְאִסוּר בִּשּׁוּל, וְאֶחָד לְאִסוּר אֲכִילָה, וְאֶחָד לְאִסוּר הֲנָאָה. וְהוֹצִיא אֲכִילָה בִּלְשׁוֹן בִּשּׁוּל, לוֹמַר שֶׁאֵינוֹ אָסוּר מִן הַתּוֹרָה אֶלָּא דֶּרֶךְ בִּשּׁוּל, אֲבָל מִדְּרַבָּנָן אָסוּר בְּכָל עִנְיָן. כָּל בָּשָׂר בְּחָלָב שֶׁאֵינוֹ אָסוּר מִן הַתּוֹרָה, מֻתָּר בַּהֲנָאָה. (טוּר וְאָרֹךְ כְּלָל ל').

It is written in the Torah: "you will not cook a kid in the milk of its mother" three times (Exodus 23:19; Exodus 34:26; Deuteronomy 14:21); once for the prohibition of cooking, once for the prohibition of eating, and once for the prohibition of receiving benefit [from the cooked meat and milk products]. The prohibition of eating is presented in the language of cooking, to say that there is no prohibition from the Torah [in regard to meat and milk] unless it is in a manner of cooking, but rabbinically it [the mixture of meat and milk] is forbidden in every way. All meat and milk [mixtures] that are not forbidden from the Torah are permitted to benefit from.

Se’if 2ב׳

גְּדִי, לָאו דַּוְקָא, דְּהוּא הַדִּין שׁוֹר, שֶׂה וָעֵז. וְלֹא שְׁנָא בַּחֲלֵב אֵם, וְלֹא שְׁנָא בַּחֲלֵב אַחֶרֶת, אֶלָּא שֶׁדִּבֵּר הַכָּתוּב בַּהֹוֶה.

[The word] "kid", is not specific, it is the same rule with ox, sheep and goat. There is no difference if it is the milk of the mother, or of another [domesticated] animal. Rather, the verse refers to the common case.

Se’if 3ג׳

אֵינוֹ נוֹהֵג אֶלָּא בִּבְשַׂר בְּהֵמָה טְהוֹרָה בַּחֲלֵב בְּהֵמָה טְהוֹרָה, אֲבָל בְּשַׂר טְהוֹרָה בַּחֲלֵב טְמֵאָה, אוֹ בְּשַׂר טְמֵאָה בַּחֲלֵב טְהוֹרָה, מֻתָּרִים בְּבִשּׁוּל וּבַהֲנָאָה. וּבְשַׂר חַיָּה וָעוֹף, אֲפִלּוּ בַּחֲלֵב טְהוֹרָה, מֻתָּר בְּבִשּׁוּל, וּבַהֲנָאָה; וְאַף בַּאֲכִילָה אֵינוֹ אָסוּר, אֶלָּא מִדְּרַבָּנָן. אֲבָל דָּגִים וַחֲגָבִים, אֵין בָּהֶם אִסוּר, אֲפִלּוּ מִדְּרַבָּנָן. הַגָּה: וְנָהֲגוּ לַעֲשׂוֹת חָלָב מִשְּׁקֵדִים וּמַנִּיחִים בָּהּ בְּשַׂר עוֹף, הוֹאִיל וְאֵינוֹ רַק מִדְּרַבָּנָן. אֲבָל בְּשַׂר בְּהֵמָה, יֵשׁ לְהַנִּיחַ אֵצֶל הַחָלָב שְׁקֵדִים, מִשּׁוּם מַרְאִית הָעַיִן, כְּמוֹ שֶׁנִּתְבָּאֵר לְעֵיל סִימָן ס"ו לְעִנְיַן דָּם (ד"ע).

The law only applies with meat from a pure [kosher] animal and milk from a pure animal, but meat of a pure animal in milk that is impure, or meat from an impure animal in pure milk, is permitted to cook and benefit from. Meat of a wild animal and of fowl, even in milk which is pure, is permitted to cook and benefit from; and even eating is only prohibited rabbinically. Fish and grasshoppers are not prohibited [with milk] even rabbinically. RAMA: We make milk from almonds and place bird meat in it, since [milk and bird meat] is only rabbinically [forbidden]. But with meat from a domesticated animal, place almonds next to the milk, so that people don't misunderstand. This is as we said above, in chapter 66.