Then Adonai said to Moses, “Rise up early in the morning and stand before Pharaoh. As he comes to the water say to him, This is what Adonai says: Let My people go, that they may serve Me.
So they took soot from the furnace and stood before Pharaoh. When Moses threw it heavenward, it became boils erupting with sores on both men and animals.
When Pharaoh inquired, there was not so much as one of the cattle of Bnei-Yisrael dead. But the heart of Pharaoh was stubborn, and he did not let the people go.