LXX Num 8:19

καὶ ἀπέδωκα τοὺς Λευείτας ἀπόδομα δεδομένους Ἀαρὼν κοὶ τοῖς υἱοῖς αὐτοῦ ἐκ μέσου υἱῶν Ἰσραὴλ, ἐργάζεσθαι τὰ ἔργα τῶν υἱῶν Ἰσραὴλ ἐν τῇ σκηνῇ τοῦ μαρτυρίου καὶ ἐξιλάσκεσθαι περὶ τῶν υἱῶν Ἰσραὴλ· καὶ οὐκ ἔσται τοῖς υἱοῖς Ἰσραὴλ προσεγγίζων πρὸς τὰ ἅγια.

And I have given the Levites as a gift to Aaron and his sons from among the Israelites, to perform the service for the Israelites at the Tent of Meeting and to make atonement on their behalf, so that no plague will come against the Israelites when they approach the sanctuary.”