Numbers 3:4-6

Complete Jewish Bible

⁴ But Nadav and Avihu died in the presence of Adonai when they offered unauthorized fire before Adonai in the Sinai Desert, and they had no children; El‘azar and Itamar served as cohanim in the presence of Aharon their father.

⁵ Adonai said to Moshe, ⁶ “Summon the tribe of Levi, and assign them to Aharon the cohen, so that they can help him.