Numbers 16:38, 40

The censers of these men who sinned against their own souls, let them be made into hammered plates as a covering for the altar. Because they presented them before the LORD, therefore they are holy; and they shall be a sign to the children of Israel.”

to be a memorial to the children of Israel that no outsider, who is not a descendant of Aaron, should come near to offer incense before the LORD, that he might not become like Korah and his companions, just as the LORD had said to him through Moses.