Exodus 9:8-12

The LORD said to Moses and Aaron, “Fill your hands with ashes from a furnace. Moses, throw the ashes into the air in front of the king of Egypt. The ashes will spread like dust through all the land of Egypt. They will cause boils to break out and become sores on the skin of people and animals everywhere in the land.” So Moses and Aaron took ashes from a furnace and went and stood before the king. Moses threw ashes into the air, which caused boils to break out and become sores on people and animals. The magicians could not stand before Moses, because all the Egyptians had boils, even the magicians. But the LORD made the king stubborn, so he refused to listen to Moses and Aaron, just as the LORD had said.