Exodus 9:8-10

8And Jehovah said to Moses and to Aaron, Take to yourselves handfuls of ashes of the furnace, and let Moses scatter it toward the heavens before the eyes of Pharaoh.

9And it shall become fine dust over all the land of Egypt, and shall become boils on man and on cattle, breaking out [with] blisters, throughout the land of Egypt.

10And they took ashes of the furnace, and stood before Pharaoh; and Moses sprinkled it toward the heavens; and it became boils [with] blisters breaking out on man and on cattle.