Leviticus 10:1-2

1Nadab and Abihu were sons of Aaron. They put hot material in the pots that they used to burn incense. They threw incense over the hot material. They offered the incense to the Lord. This was a wrong thing to do. The Lord had not told them that they should do it. So it was wrong.

2The Lord was angry and he sent fire to burn them. They died there in front of the Lord's altar.