Charles Ellicott Commentary Numbers 3:4

"And Nadab and Abihu died before Jehovah, when they offered strange fire before Jehovah, in the wilderness of Sinai, and they had no children; and Eleazar and Ithamar ministered in the priest`s office in the presence of Aaron their father." — Numbers 3:4 (ASV)

Died before the Lord. —The account is given in Leviticus 10:1-2, where the same expression “before the Lord” is used both in regard to the offering of strange fire by Nadab and Abihu, and also in regard to their death.

And they had no children. —To die childless was regarded not only as a reproach, but also as a judgment. This was especially the case in regard to Nadab and Abihu, inasmuch as the sons of one, or of both (as was the case in regard to the sons of Eleazar and of Ithamar), would have succeeded to the high priesthood.