The Ancient Khurasan:
The ancient Khurasan was the last eastern province of the Persian Empire. Khurasan, in Persian, means the “land of the sunrise”, a natural synonym for East. The term was loosely applied to territories of Persia east and north east of Dasht-e-Kavir.
Emperor Babur wrote in his memoirs  that Indians used to call all non-Indians as Khurasanis. Regarding the boundary of Hindustan (India) and Khurasan, it is written: “On the road between Hindustan and Khurasan, there are two great marts: the one Kabul, the other Kandahar.”
In modern day world the ancient Khurasan is divided into five central Asian countries i.e.
The largest part of the ancient Khurasan is in Afghanistan today.
The present day cities of these modern countries would give a better idea of the geographical map of the ancient Khurasan. These cities include:
1. Nishapur and Tus in Iran.
2. Herat, Balkh, Ghazni and Kabul in Afghanistan
3. Khujand and Panjakent in Tajikistan
4. Merv and Sanjan in Turkmenistan
5. Samarqand and Bukhara in Uzbekistan
Ghulam Mohammad Ghubar, an ethnic Tajik scholar and historian from Afghanistan, talks of Proper Khurasan and Improper Khurasan in his book titled “Khurasan”. According to him, Proper Khurasan contained regions lying between Balkh (in the East), Merv (in the North), Sijistan (in the South), Nishapur (in the West) and Herat, known as The Pearl of Khurasan, in the center. While Improper Khurasan’s boundaries extended to Kabul and Ghazni in the East, Balochistan and Zabulistan in the South, Transoxiana and Khwarezm in the North and Damaghan and Gurgan in the West.
Khurasan in Islamic Prophecies:
Khurasan plays an important role in the Islamic prophecies of end times, the wars before appearance of Dajjal and the second coming of Jesus Christ (‘Eesa alayhissalaam).
One must wonder why Afghanistan has been the centre stage of the world for more than three decades now. What is there in the barren land of rugged mountains of Afghanistan that attracted almost every super power in the course of history?
Every super power in the world, since the time of Alexander the Great till the United States, have turned to Afghanistan when it was their turn to fall from grace.
God has His own ways of making histories and turn fates.
We have already established that Afghanistan has the most land area of ancient Khurasan in it. The Islamic prophecies that speak of the appearance of Imam Mehdi also speak of an army of black flags from Khurasan that will come to help Imam Mehdi to establish his Caliphate in the Holy Ka’abah.
“ Narrated by Hazrat Abdullah bin Masood (radhiyallahu anhu) that Prophet (sallallaahu alayhi wasallam) said: A Nation will come from the east with black flags and they will ask for some “Khair” (because of them being needy) but the people will not give them, then, they will fight and win over those people (who did not give them what they asked). Now the people will give them what they asked for but they will not accept it until they will hand it over to a person from my progeny who will fill this earth with justice just as it was previously filled with oppression and tyranny. So if anyone of you finds this nation (i.e. from the east with black flags) then you must join them even if you have to crawl over ice” 
We have to keep in mind that the holy Prophet Muhammad (sallallaahu alayhi wasallam) lived most his life in Makkah and the last 10 years in Madinah in present day Saudi Arabia. Geographically there are only three Muslim countries, today, in exact east of Saudi Arabia i.e. Iran, Afghanistan and Pakistan. So it becomes easy for us to establish that whoever this army of black flags is, it belongs to one or more of these three countries.
Another Hadith says:
“Abu Huraira (radhiyallahu anhu) reported Allah’s Apostle (sallallaahu alayhi wasallam) saying: You have heard about a city; the one side of which is in the land and the other is in the sea (Constantinople). They said: Allah’s Messenger, Yes. There upon he said: The last hour would come unless seventy thousand persons from Bani Ishaq would attack it. When they would land there, they will neither fight with weapons nor would show arrows but would only say: There is no god but Allah and Allah is the Greatest, that one side of it would fall. Thaur (one of the narrators) said: I think that he said: The part by the side of the ocean. Then they would say for the second time: There is no god but Allah and Allah is the Greatest that the second side would also fall, and they would say: There is no god but Allah and Allah is the Greatest, that the gates would be opened for them and they would enter therein and, they would be collecting spoils of war and distributing them amongst themselves that a noise would be heard and it would be said: Verily, Dajjal has come. And thus they would everything there and would turn to him.” 
Constantinople is present day Istanbul and this particular Hadith verifies that it would be either siding with Anti-Imam Mehdi forces or would be occupied by Non-Muslims in the time of Imam Mehdi. From other Ahadith we get clarified that this attack on Istanbul by seventy thousand people of Bani Ishaq or the descendants of Prophet Isaac (alayhissalaam) would be led by Imam Mehdi himself. In the language of Ahadith seventy thousand means a very large number, it may or may not be actually seventy thousand. The descendants of Prophet Isaac (alayhissalaam) have been referred with different names in religious scriptures and in different Ahadith i.e. Aal-e-Haroon, Nation of Liberated Slaves and Bani-Israel.
Israel is the alternate name of Prophet Ya’qub (alayhissalaam) (Biblical Jacob) who was the son of Prophet Ishaaq (alayhissalaam)(Biblical Isaac). Haroon (alayhissalaam) or Aaron was the brother of Musa (alayhissalaam) (Moses) and both of them were descendants of Ishaaq (alayhissalaam) and Ya’qub (alayhissalaam). So the army of Imam Mehdi will be from the descendants of Prophet Ishaq (alayhissalaam) and Ya’qub (alayhissalaam) or popularly Bani-Israel.
Now, the very term Israel itself hints of the present day Jewish nation-state of Israel and one would ask why Israel would help Imam Mehdi. No, they certainly will not. This army of Imam Mehdi that will come from the East, with black flags, will be from Bani-Israel who would already be Muslims.
One of the Ahadith further elaborate:
“Narrated by Abdur Rehman Al-Jarshi that I heard companion of Prophet (sallallaahu alayhi wasallam), Hazrat Amr Bin Marra Al-Jamli (radhiyallahu anhu) that Prophet (sallallaahu alayhi wasallam) said: Surely Black Flags will appear from the Khurasan until the people (under the leadership of this flag) will tie their horses with the Olive Trees between Bait-e-Lahya and Harasta. We asked are there any Olive trees between these places: He said, “If there isn’t then soon it will grow so that those people (of Khurasan) will come and tie their horses there.” (4)
Another of the Ahadith says:
“Abu Huraira (radhiyallahu anhu) says that Rasulullah (sallallaahu alayhi wasallam) said: (Armies carrying) black flags will come from Khurasan, no power will be able to stop them and they will finally reach Eela (Aqsa Mosque in Jerusalem) where they will erect their flags” (5)
Interestingly, another Hadith says:
“Anas ibn Malik narrated that Allah’s Apostle (sallallaahu alayhi wasallam) said: The Dajjal would be followed by seventy thousand Jews of Isfahan wearing Persian shawls.” (6)
Now, from the above three Ahadith we can establish that the army of Mehdi will consist of Muslims from Bani-Israel from Khurasan holding black flags. No power in the world will be able to stop them till they reach Jerusalem and erect their flags where there is Aqsa Mosque standing today.
Dajjal will also have an army of Bani-Israel. Both Muslim and Christian sources (other than evangelical Christians) establish that the Anti-Christ will be a Jewish Leader. The Hadith of the Prophet Muhammad (sallallaahu alayhi wasallam) clears that the Dajjal will have an army of Persian Jews from Isfahan. Interestingly, Iran supports the largest Jewish population in the Muslim world of approximately 40,000 mainly in Tehran, Isfahan and Shiraz.  It has already been said that in Hadith language 70 thousands mean a very large number that may or may not be actually 70 thousand.
This leaves us with the judgment that Imam Mehdi will lead an army of Muslim Bani-Israel from Khurasan and Dajjal will lead an army of Jew Bani-Israel from Isfahan.
Research Paper by Bilal Khan
Israel and the Lost Tribes:
In order to find out who these Muslims Bani-Israel from Khurasan are, it would be important to critically examine the history of Israelites.
Prophet Jacob or Hazrat Ya’qoob (alayhissalaam) in Arabic, was the son of Prophet Isaac or Ishaq (alayhissalaam) in Urdu and grandson of Prophet Abraham (Qur’anic Ibraheem alayhissalaam). He was popularly known by his alternate name “Israel”. All of his children were subsequently called Bani-Israel or Israelites i.e. the descendants of Israel (Jacob).
Prophet Jacob (Ya’qub alayhissalaam) had twelve sons, one of which was Prophet Joseph or Hazrat Yousuf (alayhissalaam) in Arabic and Prophet Joseph (Yousuf alayhissalaam) had two sons. The Bani-Israel, consequently, are divided into thirteen tribes i.e. eleven from Prophet Jacob (Ya’qub alayhissalaam) and two from Prophet Joseph (Yousuf alayhissalaam). The names of these sons of Jacob (Ya’qub alayhissalaam) and Joseph (Yousuf alayhissalaam), which are in turn the names of the tribes of Bani-Israel, are:
12. Ephraim (son of Joseph)
13. Manasseh (son of Joseph)
According to Bible, the descendants of Jacob (AS) united to form the first united Monarchy or Kingdom of Israel in approximately 1050 BCE. King David, or known as Prophet David or Hazrat Dawood (alayhissalaam) to Muslims, was the second King of this Kingdom and also the father of the famous King Solomon or Hazrat Suleiman (alayhissalaam) for Muslims. David (Dawood alayhissalaam) and his son Solomon (Suleiman alayhissalaam) constructed the Temple Mount of the Jews on Mount Moriah in Jerusalem. This temple is also known as the First Temple. The temple was destroyed by Nebuchadnezzar II of Babylon in 597 BCE. Nebuchadnezzar II not only destroyed the temple and conquered Jerusalem but also took the Jewish people along with him as slaves to Babylon where they stayed until Cyrus the Great (the founder of ancient Persian Empire) destroyed Babylon. The Persians allowed the Jews to return to the Holy Land where they constructed the Temple Mount again in 516 BCE known as Second Temple until the Temple was destroyed again by the Romans in 70 CE.
Interestingly, in 722 BCE the Assyrians under Shalmaneser V and then under Sargon II conquered the northern Kingdom of Israel, destroyed its capital Samaria and sent the Israelites into exile and captivity in Khurasan.
In Jewish popular culture, the ten tribes disappeared from history, leaving only the tribes of Benjamin, Judah and Levi to become the ancestors of modern day Jews.
Today, many ethnic groups claim descent from the lost tribes of Israel. Let us see who among them is located in the geographical Khurasan and are Muslims as well (to keep our track to find the army of Imam Mehdi).
1. Bene-Ephraim in Southern India – are Jews.
2. Bnei-Menashe in Northeast India – are Jews.
3. Beta Israel in Ethiopia – are Jews.
4. Persian and Bukharan Jews in Isfahan, Iran – are Jews.
5. Igbo of Nigeria – are Jews.
7. Samaritans in Israel – are Jews
8. The Lemba tribe in South Africa – religious practice similar to Jews.
9. House of Israel in Ghana – are Jews
10. Pashtuns or Pathans in Afghanistan/Pakistan – are Muslims
11. Kashmiris in Indo-Pakistan – are Muslims
12. Jews of Kaifeng – are Jews
In all these ethnic groups, there are only two groups that are Muslims and only one group that is geographically present in Khurasan i.e. the Pathans of Afghanistan and Pakistan. The only group that is warlike, undefeated and untamed throughout the course of history, staunch in religious fervor, filled with honor and pride and is unforgiving of its enemy; one that will fight its enemy until one of them is dead.
Research Paper by Bilal Khan