Exodus 9:8-10

8Then the Lord said to Moses and Aaron, “Take handfuls of soot from a furnace, and have Moses throw it into the air while Pharaoh is watching.

9It will become fine dust over the whole land of Egypt and will cause boils to break out and fester on both people and animals in all the land of Egypt.”

10So they took soot from a furnace and stood before Pharaoh, Moses threw it into the air, and it caused festering boils to break out on both people and animals.