Then the Lord said to Moses and Aaron, "Take handfuls of furnace soot, and Moses is to throw it toward heaven in the sight of Pharaoh.
References for Exodus 9:8
It will become fine dust over the entire land of Egypt. It will become festering boils on people and animals throughout the land of Egypt."
So they took furnace soot and stood before Pharaoh. Moses threw it toward heaven, and it became festering boils on man and beast.
The magicians could not stand before Moses because of the boils, for the boils were on the magicians as well as on all the Egyptians.
But the Lord hardened Pharaoh's heart and he did not listen to them, as the Lord had told Moses.