Whoever visited him was urged, in the most pressing terms, to enlist under the Black Standard hoisted by Mullá Ḥusayn. It was the same standard of which Muḥammad, the Prophet of God, had thus spoken: “Should your eyes behold the Black Standards proceeding from Khurásán, hasten ye towards them, even though ye should have to crawl over the snow, inasmuch as they proclaim the advent of the promised Mihdi, the Vicegerent of God.” That standard was unfurled at the command of the Báb, in the name of Quddús, and by the hands of Mullá Ḥusayn. It was carried aloft all the way from the city of Mashhad to the shrine of Shaykh Tabarsi. (The Dawn-Breakers, p. 351)
The narration (bolded text) quoted above is well-known and accepted among Muslims – Shias and Sunnis alike.
Here is the same narration presented from a Muslim source:
The Messenger of Allah, peace be upon him, said: “When the black flags come from Khurasan, go to them, for among them is the khalifah of Allah, the Mahdi.” (Imam Al Mahdi, the Twelfth Khalifah in the Sahih Sunni Ahadith)
So where is Khurasan?
In that case, where is Khurasan? The researcher easily notices that on the world map today, all the places called Khurasan are in the Islamic Republic of Iran. There used to be the Khurasan province until 2004, when it was divided into South Khurasan, North Khurasan and Razavi Khurasan. However, in ancient times, the word “Khurasan” covered a vast territory now lying in northeastern Iran, southern Turkmenistan and northern Afghanistan. (Imam Al Mahdi, the Twelfth Khalifah in the Sahih Sunni Ahadith)
Mashhad, a northeastern city of Iran, is not only located in the Razavi Khurasan province, but also included the vast territory of Greater Khorasan – the historical region. See map below.
Note: Khurasan is an alternative spelling of Khorasan and on the map, “Mashhad” is underlined in red and included in the pink region representing Greater Khurasan.