Exodus 9:8-11

8Then the LORD said to Moses and Aaron, “Take handfuls of soot from the furnace; in the sight of Pharaoh, Moses is to toss it into the air. 9It will become fine dust over all the land of Egypt, and festering boils will break out on man and beast throughout the land.”

10So they took soot from the furnace and stood before Pharaoh. Moses tossed it into the air, and festering boils broke out on man and beast. 11The magicians could not stand before Moses, because the boils had broken out on them and on all the Egyptians.