Exodus 9:8-12 NLT

8 Then the LORD said to Moses and Aaron, “Take handfuls of soot from a brick kiln, and have Moses toss it into the air while Pharaoh watches.
9 The ashes will spread like fine dust over the whole land of Egypt, causing festering boils to break out on people and animals throughout the land.”
10 So they took soot from a brick kiln and went and stood before Pharaoh. As Pharaoh watched, Moses threw the soot into the air, and boils broke out on people and animals alike.
11 Even the magicians were unable to stand before Moses, because the boils had broken out on them and all the Egyptians.
12 But the LORD hardened Pharaoh’s heart, and just as the LORD had predicted to Moses, Pharaoh refused to listen.