Mustadrak al-Hakim — Hadith 8696

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The Hour will not be established until the Romans land at al-A'maq (in al-Sham). An army will come out of Madinah to face them, from the best of the people of the earth at that time. When they line up in ranks, the Romans will say: Stand aside from between us and those who took our people captive, so that we may fight them. The Muslims will say: By Allah! We will never stand aside from between you and our brothers. So they will fight them. A third (of the Muslim army) will flee, whose repentance Allah will never accept; a third will be killed, who will be the best of martyrs in the sight of Allah; and a third will be granted victory, who will never be put to trial. Then they will reach Constantinople and conquer it. While they are dividing their spoils, having hung their weapons on the olive trees, Satan will suddenly cry out that the Messiah (the Dajjal) has reached your families behind you, though this news will be false. When they reach al-Sham, (the Dajjal) will emerge. Then, while they are preparing for battle and straightening their ranks, the iqamah will be called for the Fajr prayer, and Isa bin Maryam (may the blessings of Allah be upon him) will descend and lead them in prayer. When the enemy of Allah (the Dajjal) sees him, he will begin to melt as salt melts (in water). Even if he were to leave him (to his state), he would melt away until he perished; but Allah Almighty will have him killed at his hand, and he will show them his blood on his spear."
This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs did not record it!