Leviticus 10:1-3 NIV

[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. [2] So fire came out from the presence of the LORD and consumed them, and they died before the LORD. [3] Moses then said to Aaron, “This is what the LORD spoke of when he said: “ ‘Among those who approach me I will be proved holy; in the sight of all the people I will be honored.’ ” Aaron remained silent.