Exodus 9:8-12

Then the LORD said to Moses and Aaron, “Take handfuls of ashes from a furnace and have Moses throw it up in the air in front of Pharaoh. The ashes will turn to soot over the whole land of Egypt. It will cause skin sores that will break out in blisters on people and animals in the whole land of Egypt.” So they took ashes from the furnace, and they stood in front of Pharaoh. Moses threw the ash up in the air, and it caused skin sores and blisters to break out on people and animals. The religious experts couldn’t stand up to Moses because of the skin sores, because there were skin sores on the religious experts as well as on all the Egyptians. But the LORD made Pharaoh stubborn, and Pharaoh wouldn’t listen to them, just as the LORD had said to Moses.