Exodus 9:6-9

6And the next day the LORD did just that. All the livestock of the Egyptians died, but not one animal belonging to the Israelites died. 7Pharaoh sent officials and found that none of the livestock of the Israelites had died. But Pharaoh’s heart was hardened,1 and he would not let the people go.

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.”