Mustadrak al-Hakim — Hadith 8714

It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that he said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Gog and Magog (Ya'juj and Ma'juj) will be let loose, and they will fall upon the people just as Allah Almighty has said: 'And they will swoop down from every height' [Surah al-Anbiya: 96]. They will spread corruption in the land, and the Muslims will take refuge in their cities and fortresses, and they will also gather their livestock with them (inside those fortresses). They will drink all the water of the earth, to the point that when one group of them passes by a river, they will drink all its water and leave it completely dry; then the group coming after them will pass by there and say: 'There used to be water here once.' Until, when no one remains (on the earth) except those besieged in the fortresses or cities, their spokesman will say: 'These people of the earth are finished; we are done with them. Now the people of the heavens remain.' Then one of them will brandish his spear and throw it towards the sky, and it will come back stained with blood, as a trial and a tribulation. While they are in this state, Allah Almighty will create worms (al-naghaf) in their necks, which will come out of their necks, and they will reach the morning all lying dead, and not a sound will be heard from them. Then the Muslims will say: 'Is there a man who will dedicate his life for Allah (and go down) to see what has become of this enemy?' Then a man from among them will go out, heedless of his life and having prepared himself to be killed. He will go down and find them lying dead, one on top of another. He will call out: 'O Muslims! Rejoice, for Allah has sufficed you against your enemy.' Then they will come out of their cities and fortresses and release their livestock to graze, and there will be no fodder for that livestock except their (Gog and Magog's) flesh. So they will eat it and grow so fat as they had never grown fat from eating even the finest vegetation."
This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs did not record it.