Exodus 9:13-18

13Then the Lord said to Moses, “Get up early in the morning, confront Pharaoh and say to him, ‘This is what the Lord, the God of the Hebrews, says: Let my people go, so that they may worship me, 14or this time I will send the full force of my plagues against you and against your officials and your people, so you may know that there is no one like me in all the earth. 15For by now I could have stretched out my hand and struck you and your people with a plague that would have wiped you off the earth. 16But I have raised you up for this very purpose, that I might show you my power and that my name might be proclaimed in all the earth. 17You still set yourself against my people and will not let them go. 18Therefore, at this time tomorrow I will send the worst hailstorm that has ever fallen on Egypt, from the day it was founded till now.