In the Quran, Muhammad taught that Zul-Qarnain - who is Alexander the Great - encountered a group of people oppressed by "Gog and Magog", and aided them as follows:
Surah 18:92-100
92 Then he travelled a ˹third˺ course
93 until he reached ˹a pass˺ between two mountains. He found in front of them a people who could hardly understand ˹his˺ language.
94 They pleaded, “O Ⱬul-Qarnain! Surely Gog and Magog are spreading corruption throughout the land. Should we pay you tribute, provided that you build a wall between us and them?”
95 He responded, “What my Lord has provided for me is far better. But assist me with resources, and I will build a barrier between you and them.
96 Bring me blocks of iron!” Then, when he had filled up ˹the gap˺ between the two mountains, he ordered, “Blow!” When the iron became red hot, he said, “Bring me molten copper to pour over it.”
97 And so the enemies could neither scale nor tunnel through it.
98 He declared, “This is a mercy from my Lord. But when the promise of my Lord comes to pass, He will level it to the ground. And my Lord’s promise is ever true.”
99 On that Day, We will let them surge ˹like waves˺ over one another. Later, the Trumpet will be blown, and We will gather all ˹people˺ together.
100 On that Day We will display Hell clearly for the disbelievers,
Above, we see that Zul-Qarnain built an iron and copper wall between two mountains to block a mountain pass, and this wall was so large that the tribes of Gog and Magog "could neither scale nor tunnel through it". And, judging by verses 98-99, there is a Day in which Allah will allow the barrier to fall, and Gog and Magog will attack.
This incident is also referenced in one other place in the Quran:
Surah 21:95-97
95 It is impossible for a society which We have destroyed to ever rise again,
96 until ˹after˺ Gog and Magog have broken loose ˹from the barrier˺, swarming down from every hill,
97 ushering in the True Promise. Then—behold!—the disbelievers will stare ˹in horror, crying,˺ “Oh, woe to us! We have truly been heedless of this. In fact, we have been wrongdoers.”
So, from the Quran, we learn that somewhere on earth, Zul-Qarnain, who is the same person that the Quran describes as having found where the sun sets and rises (Surah 18:83-91), has contained a violent army, which, when loosed by Allah, will cause great suffering.
From the Hadith, we can see even more explicitly that Muhammad taught that Gog and Magog breaching their barrier was a sign of the end times:
Sahih Muslim 2901a
Hudhaifa b. Usaid al-Ghifari reported:
Allah's Messenger (ﷺ) came to us all of a sudden as we were (busy in a discussion). He said: What do you discuss about? They (the Companions) said. We are discussing about the Last Hour. Thereupon he said: It will not come until you see ten signs before and (in this connection) he made a mention of the smoke, Dajjal, the beast, the rising of the sun from the west, the descent of Jesus son of Mary (Allah be pleased with him), the Gog and Magog, and land-slides in three places, one in the east, one in the west and one in Arabia at the end of which fire would burn forth from the Yemen, and would drive people to the place of their assembly.
This is also narrated in Sahih Muslim 2901b-d, Sunan ibn-Majah 4055, and Sunan abu-Dawud 4311.
And, in keeping with his theme that the Last Hour was near, Muhammad taught that the barrier withholding Gog and Magog had been weakened or damaged during the time he was alive, and consequently, the terror they would bring was "nearly approaching":
Sahih al-Bukhari 7059
Narrated Zainab bint Jahsh:
The Prophet (ﷺ) got up from his sleep with a flushed red face and said, "None has the right to be worshipped but Allah. Woe to the Arabs, from the Great evil that is nearly approaching them. Today a gap has been made in the wall of Gog and Magog like this." (Sufyan illustrated by this forming the number 90 or 100 with his fingers.) It was asked, "Shall we be destroyed though there are righteous people among us?" The Prophet (ﷺ) said, "Yes, if evil increased."
This is also narrated in Sahih al-Bukhari 3346-47, 3598, 5293, 7135-36, Sahih Muslim 2880a-d, 2881, 2937a, and Sunan ibn-Majah 3953.
But, what's stopping them from invading? Haven't they managed to dig around, or walk around, Zul-Qarnain's wall yet, at some point in the last 1,400 years? No, because Allah keeps them in a state of confusion, and miraculously repairs the wall that Zul-Qarnain built, every day, until one day he will allow them to breach the wall, and they will attack the whole world, and even the people of the sky:
Sunan ibn-Majah 4080
It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:
"Gog and Magog people dig every day until, when they can almost see the rays of the sun, the one in charge of them says: "Go back and we will dig it tomorrow." Then Allah puts it back, stronger than it was before. (This will continue) until, when their time has come, and Allah wants to send them against the people, they will dig until they can almost see the rays of the sun, then the one who is in charge of them will say: "Go back, and we will dig it tomorrow if Allah wills.' So they will say: "If Allah wills."
Then they will come back to it and it will be as they left it. So they will dig and will come out to the people, and they will drink all the water. The people will fortify themselves against them in their fortresses. They will shoot their arrows towards the sky and they will come back with blood on them, and they will say: "We have defeated the people of earth and dominated the people of heaven." Then Allah will send a worm in the napes of their necks and will kill them thereby.'" The Messenger of Allah (ﷺ) said: "By the One in Whose Hand is my soul, the beasts of the earth will grow fat on their flesh."
This is also narrated in Sahih Muslim 2937b, and Sunan ibn-Majah 4075, 4079, 4081.
And, when they finally arrive, there will be so many of them that they will be able to drink the entire Lake of Tiberias (Sahih Muslim 2937a, Sunan ibn-Majah 4075), and Muslims will use their bows, arrows, and shields as firewood, for 7 years afterward (Sunan ibn-Majah 4076).
There are also narrations which indicate that for every Muslim, there will be 1,000 people from Gog and Magog:
Sahih al-Bukhari 4741
(When the Prophet (ﷺ) mentioned this), the people were so distressed (and afraid) that their faces got changed (in color) whereupon the Prophet (ﷺ) said, "From Gog and Magog nine-hundred ninety-nine will be taken out and one from you. You Muslims (compared to the large number of other people) will be like a black hair on the side of a white ox, or a white hair on the side of a black ox, and I hope that you will be onefourth of the people of Paradise."
This is also narrated in Sahih al-Bukhari 3348, 6530.
So, what can we make of the Quran and Hadith's accounts of Gog and Magog? Obviously, building a wall of iron big enough to block a mountain pass, which massive tribes of savage warriors cannot scale or dig around, would be prohibitive even today, let alone for Zul-Qarnain. There is a reason dams are built with reinforced concrete, not solid metal.
Also, in modern times, we can see the entire earth with satellites, and know that there is no wall, and no vast, savage tribes, waiting to destroy all peoples of the earth, each day barely held back by a miraculous repair to Zul-Qarnain's wall. So, all of this was fake, and Muhammad was a liar and a false prophet.
The Quran's account of an actual Muslim man, Zul-Qarnain, building a wall to hold back Gog and Magog, is what grounds the story in history. Because of the way it's presented, Gog and Magog cannot be dismissed as merely symbolic, or spiritual. The Hadith further ground Gog and Magog as physical tribes, and make the situation even more impossible.
This story was something that Muhammad was able to deceive people with, during his time, because they could not verify what he was saying. It's false. Muslims, wake up.