Shemot 9:9-10

And it shall become fine dust in kol Eretz Mitzrayim, and shall be a sh'khin (boil) breaking forth with festers upon adam, and upon behemah, throughout kol Eretz Mitzrayim. And they took piach of the furnace, and stood before Pharaoh; and Moshe sprinkled it up toward Shomayim; and it became a sh'khin breaking forth with festers upon adam, and upon behemah.