Numbers 3:4

But Nadab and Abihu died in the presence of the Lord when they offered strange (unholy, unacceptable, inappropriate) fire before the Lord in the Wilderness of Sinai; and they had no sons. So Eleazar and Ithamar served as priests in the presence and under the supervision of Aaron their father.

Leviticus 10:1-2

Now Nadab and Abihu, the sons of Aaron, took their respective [ceremonial] censers, put fire in them, placed incense on it and offered strange (unauthorized, unacceptable) fire before the Lord, [an act] which He had not commanded them to do.

Numbers 26:61

But Nadab and Abihu died [in the presence of God] when they offered [in their ceremonial censers] strange [unholy, unacceptable, unauthorized] fire before the Lord.

Treasury of Scripture Knowledge

Summary

Numbers 3:4

And Nadab and Abihu died before the LORD, when they offered strange fire before the LORD, in the wilderness of Sinai, and they had no children: and Eleazar and Ithamar ministered in the priest's office in the sight of Aaron their father.

General references

Numbers 26:61

Joshua 21:10

Bible References

General references

But Nadab and Abihu died [in the presence of God] when they offered [in their ceremonial censers] strange [unholy, unacceptable, unauthorized] fire before the Lord.

and they were for the sons of Aaron, one of the families of the Kohathites, of the sons of Levi, because the lot fell to them first.