The Appearance of Gog and Magog - Imam Ibn Kathir

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.

* The Gog and Magog were also known as the Scythians, a Iranian-Mongolian race, who were the ancestors of the Slavs. According to Imam al Qurtubi the Yajjuj & Majuj are the Slavs, to which today the Russians, the Serbs, the Croats, and most of the Eastern Europeans belong to. These Slavs were known for their savageness for generations.

Herodotus, the prominent Greek historian who lived before Esa ibn Maryam[as], visited the lands of the Scythians and described their way of life and savagery in great details in his book. These Scythians lived in the regions North of the Kavkaz mountains in what today is around the Black Sea, Ukraine and European Russia. They frequently made in roads and raids in regions south of the Kavkaz. The wall which Dhul Qarnain constructed was somewhere in this mountain range, and Imam Qurtubi mentions that amongst the tribes of Gog and Magog, one tribe remained outside of the wall, and they were referred as the "Turks" [those Turks were different than Turks of today who are mostly Muslims today and from amongst our brethern].
Here are some of the Scythians drawn on ancient Iranian inscriptions:

Please see post named: Following and Passing Rulings On Da'eef Ahadeeth