Numbers 16:38, 40

the censers of the men who sinned at the cost of their lives. Hammer the censers into sheets to overlay the altar, for they were presented before the LORD and have become holy. Let them be a sign to the Israelites.”

as the LORD directed him through Moses. This was to remind the Israelites that no one except a descendant of Aaron should come to burn incense before the LORD, or he would become like Korah and his followers.