Leviticus 10:1; Leviticus 10:6

1 Aaron’s sons Nadab and Abihu took their censers, put fire in them and added incense; and they offered unauthorized fire before the LORD, contrary to his command.

6 Then Moses said to Aaron and his sons Eleazar and Ithamar, “Do not let your hair become unkempt and do not tear your clothes, or you will die and the LORD will be angry with the whole community. But your relatives, all the Israelites, may mourn for those the LORD has destroyed by fire.