Reference for Nedarim 4:3
וְתוֹרֵם אֶת תְּרוּמָתוֹ וּמַעַשְׂרוֹתָיו לְדַעְתּוֹ. וּמַקְרִיב עָלָיו קִנֵּי זָבִין, קִנֵּי זָבוֹת, קִנֵּי יוֹלְדוֹת, חַטָּאוֹת וַאֲשָׁמוֹת, וּמְלַמְּדוֹ מִדְרָשׁ, הֲלָכוֹת וְאַגָּדוֹת, אֲבָל לֹא יְלַמְּדֶנּוּ מִקְרָא. אֲבָל מְלַמֵּד הוּא אֶת בָּנָיו וְאֶת בְּנוֹתָיו מִקְרָא, וְזָן אֶת אִשְׁתּוֹ וְאֶת בָּנָיו אַף עַל פִּי שֶׁהוּא חַיָּב בִּמְזוֹנוֹתֵיהֶם. וְלֹא יָזוּן אֶת בְּהֶמְתּוֹ, בֵּין טְמֵאָה בֵּין טְהוֹרָה. רַבִּי אֱלִיעֶזֶר אוֹמֵר, זָן אֶת הַטְּמֵאָה, וְאֵינוֹ זָן אֶת הַטְּהוֹרָה. אָמְרוּ לוֹ, מַה בֵּין טְמֵאָה לִטְהוֹרָה. אָמַר לָהֶן, שֶׁהַטְּהוֹרָה נַפְשָׁהּ לַשָּׁמַיִם וְגוּפָהּ שֶׁלּוֹ, וּטְמֵאָה נַפְשָׁהּ וְגוּפָהּ לַשָּׁמָיִם. אָמְרוּ לוֹ, אַף הַטְּמֵאָה נַפְשָׁהּ לַשָּׁמַיִם וְגוּפָהּ שֶׁלּוֹ, שֶׁאִם יִרְצֶה, הֲרֵי הוּא מוֹכְרָהּ לְגוֹיִם אוֹ מַאֲכִילָהּ לִכְלָבִים:
And he may tithe his terumah and his ma'aseroth to his knowledge [As when he said: "All who wish to tithe (my produce) may come and do so." But he may not tell him to do so, for he thereby makes him his messenger, and he derives pleasure through the other's doing his bidding], and he may sacrifice for him the bird offerings of zavin, zavoth, and women who have given birth [A Cohein from whom an Israelite has bevowed benefit may sacrifice these offerings for him.], and he may teach him medrash [Sifra, and Sifrei, which is the medrash of the verses], halachoth ["halachoth to Moses from Sinai"], and aggadoth [the words of the sages, which they linked to the verses. The reason he is permitted to teach him all these is that one is not permitted to take pay for teaching these, and there is no "benefit," for he is (simply) performing a mitzvah.], but he may not teach him Scripture. [For it is permitted to take pay for the teaching of Scripture; for he takes it only for the teaching of the proper cantillation of the verses. Since this is not a mitzvah of the Torah, it is permitted to take pay for it, and if he does not take it, he is found to have benefitted him. And this applies only in a place where it is customary to be paid for teaching cantillation; but in a place where it is not customary to be paid, it is permitted to teach him cantillation, too.] But he may teach his sons and his daughters Scripture [Even though it is a mitzvah for the father to teach his son, so that he thereby relieves him of his obligation, this is not called "benefitting," for "mitzvoth were not given for 'benefitting.'" And it is also possible that he could find another to teach him gratis.], and he may feed his wife and his children even though he himself is obliged to feed them; but he may not feed his beast, whether clean or unclean. [For he wishes it to be fattened and he benefits thereby.] R. Eliezer says: He may feed the unclean beast, but not the clean one. They asked him: What is the difference between the unclean and the clean? He answered: The clean one — its soul goes to heaven, and its body goes to him. The unclean one — both its soul and its body go to heaven. [For it is used for working and he is not concerned about its being fattened. They replied: The unclean one, too — its soul goes to heaven, and its body is his; for if he wishes, he can sell it to a non-Jew [for food and receive more for its having been fattened], or he can feed it to the dogs.