God the Exalted says:

“Pharaoh proclaimed to his people, ‘My people, do I not possess the dominion of Egypt, with these rivers flowing beneath me? Can you not see? Or am I not better than this despicable man who can scarcely articulate himself? Why, then, have bracelets of gold not been cast upon him, or angels come with him in close ranks?’ Thus he deluded his people and they obeyed him; they were indeed a defiantly disobedient folk. When they provoked Us to wrath, We exacted vengeance upon them and drowned them all together, making them a precedent and an example for those who would come later.” (al-Zukhruf 43:51–56)

He, Most High, also says:

“He showed him the greatest sign, but he denied and disobeyed. Then he turned away, striving, gathered his people and called out, saying, ‘I am your highest lord.’ So Allah seized him with the punishment of the Hereafter and the first life. Surely in that is a lesson for whoever fears.” (al-Nāziʿāt 79:20–26)

And He says:

“We certainly sent Moses with Our signs and a manifest authority to Pharaoh and his chiefs, but they followed Pharaoh’s command—and Pharaoh’s command was not rightly guided. He will lead his people on the Day of Resurrection and will bring them to the Fire—how wretched is the watering place to which they are led! And they were pursued in this world by a curse, and on the Day of Resurrection—how evil is the gift that is given.” (Hūd 11:96–99)

The purpose is to expose the falsity of Pharaoh’s words, “I only show you what I see,” and his claim, “I only guide you to the path of rectitude.” Concerning this the believing man said:

“My people, I fear for you a fate like the day of the confederates, like the case of the people of Noah, ʿĀd, Thamūd, and those who came after them; and Allah does not will injustice for His servants. My people, I fear for you the Day of Summoning, the day you will turn to flee, but you will have no protector against Allah. Whoever Allah leads astray, none can guide. Joseph came to you before with clear proofs, yet you remained in doubt about what he brought until, when he perished, you said, ‘Allah will never send a messenger after him.’ Thus Allah leaves astray everyone who is immoderate and given to doubt—those who dispute Allah’s signs without any authority having come to them. That is exceedingly hateful in the sight of Allah and of those who believe. Thus does Allah seal the heart of every arrogant tyrant.” (Ghāfir 40:29–35)

Allah’s ally was warning them that, should they belie the Messenger of Allah Moses, the same scourges and exemplary punishments that struck earlier nations would befall them—punishments whose reports had reached them concerning the people of Noah, ʿĀd, Thamūd, and those who followed up to their own time. Through such chastisements Allah has established proof for all the inhabitants of the earth: He annihilated the enemies who rejected the prophets and saved the allies who followed them. He likewise frightened them with the mention of the Day of Resurrection, called “the Day of Summoning,” that is, the day when people will cry out to one another while trying—if it were possible—to flee, though there will be no escape: “On that Day man will say, ‘Where can I flee?’ No indeed! There is no refuge. To your Lord on that Day will be the final abode.” (al-Qiyāmah 75:10–12)

The Exalted also says:

“O company of jinn and humankind, if you are able to pass beyond the regions of the heavens and the earth, then pass—but you will not pass except by an authority. So which of your Lord’s favors will you deny? A flame of fire and molten copper will be loosed upon you, and you will not prevail. So which of your Lord’s favors will you deny?” (al-Raḥmān 55:33–36)

Some of the reciters pronounce it “the Day of Summōning” (with a doubled d), meaning the Day of Flight; it may also be a designation for the Day of Resurrection.