Exodus 9:14

10 So they took soot from the furnace and stood before Pharaoh. Moses tossed it into the air, and festering boils broke out on man and beast.

11 The magicians could not stand before Moses, because the boils had broken out on them and on all the Egyptians.

12 But the LORD hardened Pharaoh’s heart, and he would not listen to them, just as the LORD had said to Moses.

13 Then the LORD said to Moses, “Get up early in the morning, stand before Pharaoh, and tell him that this is what the LORD, the God of the Hebrews, says: ‘Let My people go, so that they may worship Me.

14 Otherwise, I will send all My plagues against you and your officials and your people, so you may know that there is no one like Me in all the earth.

15 For by this time I could have stretched out My hand and struck you and your people with a plague to wipe you off the earth.

16 But I have raised you up for this very purpose, that I might display My power to you, and that My name might be proclaimed in all the earth.

17 Still, you lord it over My people and do not allow them to go.

18 Behold, at this time tomorrow I will rain down the worst hail that has ever fallen on Egypt, from the day it was founded until now.

Read all of Exodus 9