Exodus 9:8-10

8 The Plague of Boils
Then the Lord said to Moses and Aaron, “Take handfuls of soot from a furnace and have Moses toss it into the air in the presence of Pharaoh.

9 It will become fine dust over the whole land of Egypt, and festering boils will break out on men and animals throughout the land.”

10 So they took soot from a furnace and stood before Pharaoh. Moses tossed it into the air, and festering boils broke out on men and animals.