Exodus 9:8-12 NLT

8 Then the LORD said to Moses and Aaron, "Take soot from a furnace, and have Moses toss it into the sky while Pharaoh watches.
9 It will spread like fine dust over the whole land of Egypt, causing boils to break out on people and animals alike."
10 So they gathered soot from a furnace and went to see Pharaoh. As Pharaoh watched, Moses tossed the soot into the air, and terrible boils broke out on the people and animals throughout Egypt.
11 Even the magicians were unable to stand before Moses, because the boils had broken out on them, too.
12 But the LORD made Pharaoh even more stubborn, and he refused to listen, just as the LORD had predicted.