Leviticus 10:1-3

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

So fire came out from the presence of the LORD and consumed them, and they died in the presence of the LORD.

Then Moses said to Aaron, “This is what the LORD meant when He said: ‘To those who come near Me I will show My holiness, and in the sight of all the people I will reveal My glory.’” But Aaron remained silent.