Exodus 9:18

Behold, at this time tomorrow I will cause to come down from the treasures of the heavens a mighty hall, the like of which hath never been in Mizraim since the day when men were settled upon it until now.

In view of the fact that Scripture states, A very grievous hail, such as hath not been in Egypt since the day it was founded, and repeats it again, Very grievous, such as had not been in all the land of Egypt since it became a nation, there is an allusion that there are other places in the world where such hail did come down, such as is mentioned in the verse, And the Eternal cast down great stones from heaven upon them, or as is mentioned in connection with [the destruction of] Sodom, brimstone, and salt, and fire. But in the land of Egypt, where there is no rain or hail, this was a great wonder.
I have not understood what is said in Midrash Rabbah: “The verse does not say, ‘as hath not been in Egypt like it,’ but instead it says, ‘as hath not been like it in Egypt,’ which means there has neither been like it in the world nor in Egypt.” And the expression, since the day it was founded, is equivalent to saying: “Your fathers and your grandfathers have never seen the like of it.” But it is not possible to say that it suggests that the like of it occurred before the world was founded or before the inception of nations. Perhaps because this hail came as a punishment upon the inhabitants of Egypt and was not in the natural order, [the verse] is saying that nothing like it has ever occurred because of the sins of the fathers, for before the inception of Egypt as a nation, surely there was no [reason for] such hail to come.

BEHOLD, TOMORROW ABOUT THIS TIME I WILL CAUSE IT TO RAIN A VERY GRIEVOUS HAIL, etc. 19. NOW THEREFORE SEND, HASTEN IN THY CATTLE. All this is G-d’s word to Moses, and it is self-understood that Moses came and told Pharaoh all the words of G-d that He sent him to speak, and there was no need to prolong the account [of Moses’ going to Pharaoh and so telling him]. Scripture only states, He that feared the word of the Eternal among the servants of Pharaoh made his servants and his cattle flee into the houses, from which it is clear that Moses had told them [G-d’s words]. This advice was on account of G-d’s being merciful to them, since the plague of hail was sent only against the produce of the earth and not against man, therefore doth He instruct sinners in the way to save them from the plague.