Numbers 16:5, 40

and he spoke to Korah and all his company, saying, “Tomorrow morning the LORD will show who is His and who is holy, and will cause him to come near to Him. That one whom He chooses He will cause to come near to Him.

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.