Exodus 9:8

9:7 Then Pharaoh sent, and indeed, not even one of the livestock of the Israelites was dead. But the heart of Pharaoh became hard, and he did not let the people go.

9:8 So the LORD said to Moses and Aaron, "Take for yourselves handfuls of ashes from a furnace, and let Moses scatter it toward the heavens in the sight of Pharaoh.

9:9 And it will become fine dust in all the land of Egypt, and it will cause boils that break out in sores on man and beast throughout all the land of Egypt."