1 Chronicles 24:1

וּלְכֹל הַעֲלוֹת עֹלוֹת לַיהוָה לַשַּׁבָּתוֹת לֶחֳדָשִׁים וְלַמֹּעֲדִים בְּמִסְפָּר כְּמִשְׁפָּט עֲלֵיהֶם תָּמִיד לִפְנֵי יְהוָֽה

and to offer all burnt-offerings unto the LORD, on the sabbaths, on the new moons, and in the appointed seasons, in number according to the ordinance concerning them, continually, before the LORD;

וְשָׁמְרוּ אֶת־מִשְׁמֶרֶת אֹֽהֶל־מוֹעֵד וְאֵת מִשְׁמֶרֶת הַקֹּדֶשׁ וּמִשְׁמֶרֶת בְּנֵי אַהֲרֹן אֲחֵיהֶם לַעֲבֹדַת בֵּית יְהוָֽה

and that they should keep the charge of the tent of meeting, and the charge of the holy place, and the charge of the sons of Aaron their brethren, for the service of the house of the LORD.

וַיָּמָת נָדָב וַאֲבִיהוּא לִפְנֵי אֲבִיהֶם וּבָנִים לֹא־הָיוּ לָהֶם וַֽיְכַהֲנוּ אֶלְעָזָר וְאִיתָמָֽר

But Nadab and Abihu died before their father, and had no children; therefore Eleazar and Ithamar executed the priest’s office.

וַיֶּֽחָלְקֵם דָּוִיד וְצָדוֹק מִן־בְּנֵי אֶלְעָזָר וַאֲחִימֶלֶךְ מִן־בְּנֵי אִיתָמָר לִפְקֻדָּתָם בַּעֲבֹדָתָֽם

And David with Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, divided them according to their ordering in their service.