They (two tribes or peoples) will appear at the time of Jesus son of Mary, after the Dajjaal. Allah will destroy them all in one night, in response to the supplication of Jesus.
Abu Hurayrah reported that the Prophet (S) said, "Every day, Gog and Magog are trying to dig a way out through the barrier. When they begin to see sunlight through it, the one who is in charge of them says, 'Go back; you can carry on digging tomorrow,' and when they come back, the barrier is stronger than it was before. This will continue until their time comes and Allah wishes to send them forth. They will dig until they begin to see sunlight, then the one who is in charge of them will say, 'Go back; you can carry on digging tomorrow, in shaa'Allah.' In this case he will make an exception by saying in shaa'Allah, thus relating the matter to the Will of Allah. They will return on the following day, and find the hole as they left it. They will carry on digging and come out against the people. They will drink all the water, and find the hole as they left it, and the people will entrench themselves in their fortresses. Gog and Magog will fire their arrows into the sky, and they will fall back to earth with something like blood on them. Gog and Magog will say, 'We have defeated the people of earth, and overcome the people of heaven.' Then Allah will send a kind of worm in the napes of their nacks, and they will be killed by it...'By Him a in Whose hand is the soul of Muhammad, the beasts of the earth will become fat.'" [Tirmidhee, Abwaab al-Tafseer: Surat al-Kahf (Hadith 5160), 8/597-99; Ibn Maajah, Kitaab al-Fitan, (Hadith 4080), 2/1364. Ahmad, Musnad, 2/510, 511.]
Gog and Magog are two groups of Turks, descended from Yaafith (Japheth), the father of the Turks, one of the sons of Noah. At the time of Abraham (AS), there was a king called Dhoo'l-Qarnayn. He performed Tawaaf around the Ka'bah with Abraham (AS) when he first built it; he believed and followed him. Dhoo'l-Qarnayn was a good man and a great king; Allah gave him great power and he ruled the east and west. He held sway over all kings and countries, and travelled far and wide in both east and west. He travelled eastwards until he reached a pass between two mountains, through which people were coming out. They did not understand anything, because they were so isolated; they were Gog and Magog. They were spreading corruption through the earth, and harming the people, so the people sought help from Dhoo'l-Qarnayn. They asked him to build a barrier between them and Gog and Magog. He asked them to him to build it, so together they built a barrier by mixing iron, copper and tar.
Thus Dhoo'l-Qarnayn restrained Gog and Magog behind the barrier. They tried to penetrate the barrier, or to climb over it, but to no avail. They could not succeed because the barrier is so huge and smooth. They began to dig, and they have been digging for centuries; they will continue to do so until the time when Allah decrees that they come out. At that time the barrier will collapse, and Gog and Magog will rush out in all directions, spreading corruption, uprooting plants, killing people. When Jesus (AS) prays against them, Allah will send a kind of work in the napes of their necks, and they will be killed by it.
Antoher relevant hadeeth:
-"Ibn Mas'ood reported that the Prophet (S) said, "On the night of the Israa' (night journey), I met my father Abraham, Moses and Jesus, and they discussed the Hour. The matter was referred first to Abraham, then to Moses, and both said, 'I have no knowledge of it'. Then it was referred to Jesus, who said, 'No one knows about its timing except Allah; what my Lord told me was that the Dajjaal will appear, and when he sees me he will begin to melt like lead. Allah will destroy him when he sees me. The Muslims will fight against the Kaafirs, and even the trees and rocks will say, "O Muslim, there is a Kaafir hiding beneath me - come and kill him!" Allah will destroy the Kaafirs, and the people will return to their lands. Then Gog and Magog will appear from all directions, eating and drinking everything they found. The people will complain to me, so I will pray to Allah and He will destroy them, so that the earth will be filled with their stench. Allah will send rain which will wash their bodies into the sea. My Lord has told me that when that happens, the HOUR WILL BE VERY CLOSE, LIKE A PREGNANT WOMAN WHOSE TIME IS DUE, BUT HER FAMILY DO NOT KNOW EXACTLY WHEN SHE WILL DELIVER."
[Ahmad, Musnad, 1/375. Similar Hadith in Ibn Maajah, Kitaab al-Fitan (hadith 4081), 2/1365, 1366]
From "The Signs Before the Day of Judgement"
Based on ibn Katheer's "Al-Bidaayah wa'l-Nihaayah" (The Beginning and the End) © Taqwa