דברים י״ח:ו׳-ח׳

וכי יבא הלוי. יָכוֹל בְּבֶן לֵוִי וַדַּאי הַכָּתוּב מְדַבֵּר, תַּלְמוּד לוֹמַר ושרת, יָצְאוּ לְוִיִּים שֶׁאֵין רְאוּיִין לְשֵׁרוּת (ספרי):

If a Levite should come. Perhaps it is literally to the Levite that Scripture refers? The Torah therefore teaches “He shall perform the service” this excludes the Levites, who are not permitted to perform the services.

ובא בכל אות נפשו, ושרת. לִמֵּד עַל הַכֹּהֵן שֶׁבָּא וּמַקְרִיב קָרְבְּנוֹת נִדְבָתוֹ אוֹ חוֹבָתוֹ וַאֲפִלּוּ בְמִשְׁמָר שֶׁאֵינוֹ שֶׁלּוֹ (בבא קמא ק"ט); דָּ"אַ — עוֹד לִמֵּד עַל הַכֹּהֲנִים הַבָּאִים לָרֶגֶל שֶׁמַּקְרִיבִין (בַּמִּשְׁמָר) וְעוֹבְדִין בַּקָּרְבָּנוֹת הַבָּאוֹת מֵחֲמַת הָרֶגֶל כְּגוֹן מוּסְפֵי הָרֶגֶל וְאַף עַל פִּי שֶׁאֵין הַמִּשְׁמָר שֶׁלָּהֶם (ספרי; סוכה נ"ה):

Coming with all his soul’s desire. He shall perform the service. This teaches, concerning the kohein, that he is permitted to come and offer up his personal voluntary or obligatory sacrifices, even during a watch which is not his own. Another interpretation. This teaches, further, that the kohanim who came during the festival [were permitted] to bring offerings with the ministering watch, by performing the sacrificial services with the offerings which were brought because of the festival obligation — for example, the festival musaf-offerings — although the watch was not their own.

חלק כחלק יאכלו. מְלַמֵּד שֶׁחוֹלְקִין בָּעוֹרוֹת וּבִּבְשַׂר שְׂעִירֵי חַטָּאוֹת, יָכוֹל אַף בִּדְּבָרִים הַבָּאִים שֶׁלֹּא מֵחֲמַת הָרֶגֶל, כְּגוֹן תְּמִידִין וּמוּסְפֵי שַׁבָּת וּנְדָרִים וּנְדָבוֹת, תַּ"לֹ לבד ממכריו על האבות חוּץ מִמַּה שֶּׁמָּכְרוּ הָאָבוֹת בִּימֵי דָּוִד וּשְׁמוּאֵל שֶׁנִּקְבְעוּ הַמִּשְׁמָרוֹת וּמָכְרוּ זֶה לָזֶה, טֹל אַתָּה שַׁבַּתְּךָ וַאֲנִי אֶטֹּל שַׁבַּתִּי (שם):

They shall eat equal portions. This teaches that they share in the skins, and in the flesh of the sin-offering goats. Perhaps even in the offerings unrelated to the festival — for example, the constant tamid and Shabbos musaf-offerings, and the endowment and gift-offerings? The Torah therefore teaches, except for what the families sold [to one another], with the exception of the matters [included] in the ancestral exchange, during the time of Dovid and Shmuel, when the watches were established. They exchanged with each other — ‘Take your Shabbos, and I will take my Shabbos.’