וְלִבְנֵ֥י אַהֲרֹ֖ן מַחְלְקוֹתָ֑ם בְּנֵ֣י אַהֲרֹ֔ן נָדָב֙ וַאֲבִיה֔וּא אֶלְעָזָ֖ר וְאִיתָמָֽר׃
Quanto ai figli di Aaronne, queste furono le loro classi. I figli di Aaronne: Nadab e Abihu, Eleazar e Itamar.
Rashi
And the priests...on their watches as David had divided them into twenty-four watches, for each watch to serve its week, and the Levites likewise on their twenty-four watches
Rashi
in the watches as we find (in I Chronicles from ch. 24 on) that the Levites were divided into twenty- four watches.