Ma’mun, the cruel and cunning Abbasid caliph in the year 201 A.H./817 forcefully exiled Imam Reza (a.s) from Medina to Marw. (The city where Mamun’s seat of caliphate was located).
According to Ma’mun’s commands the direction of Imam Rida (a.s) caravan from Medina to Marw was predetermined. Holy Imam (a.s) had to pass through some towns and villages. He arrived in Marw on the 10th of Shawwal in 201 A.H./ 1 May 817, via Basrah, Khorramshahr, Ahwaz, Rey, Neyshabur, Sanabad and Sarakhs. Throughout his long journey the Holy Imam (a.s) was cordially received by the people living in those cities and villages on the route.
The most interesting incident during the journey occurred in Neyshabur. The great metropolis of Neyshabur, during that time was one of the most important and leading centers of Islamic learning, where large number of jurisprudents and scholars of Hadith were residing in that city.
The day His Holiness was sitting in a litter placed on a mule and passing through the avenues in Neyshabur, throngs of people estimated more than 120.000 earnestly gathered round his retinue, and there thousands of distinguished scholars and narrators present among the crowd requested the Holy Imam (a.s) to narrate a Hadith.
Accepting their request His Holiness ordered his men to draw the reins of his mule, and then the Holy Imam (a.s) drew the hanging curtain of his litter aside.
On beholding the holy visage of Imam Rida (a.s) the witnessing people present there suddenly burst into tears of joy and happily cried out. Some of them tore their robes and knelt to kiss the stirrup of the mule on which the Holy Imam’s litter had been placed.
What a public uproar of admiration!!
Nothing could extinguish the fiery applause of the huge multitude assembled there.
Then Imam Rida (a.s), looked at that great congregation and said: Musa ibn Ja’ffar (a.s), my dignified father once quoted the words of his father Ja’ffar ibn Muhammad Sadiq (a.s), who in his turn related the words of his father Muhammad ibn Ali (a.s), who narrated the words of his father Ali ibn Husayn (a.s), who likewise quoted Husayn (a.s), the master of the youth residing in paradise, who directly quoted the Holy Messenger of Allah (s.a.w.), who narrated the words of Gabriel (a.s), who quoted the divine words of the Exalted Lord as follows:
“There is no God but Allah, the One is My stronghold in which the reciter of this holy verse can enter and then he will dwell there safely, and will not suffer My wrath”
The people who had assembled round the Imam’s litter thought that His Holiness’ talk was over, but to their amazement the Holy Imam (a.s) appeared from behind the litter curtain again and added the following words to what he had previously stated:
“But all this depends on some conditions, and I am considered to be one of those conditions”.
This historical and the most famous Hadith Qudsi is called “SILSILATUL DHAHAB”. Imam Rida (a.s) confirms that worshipping God will be counted as a perfect procedure when it is based on the obedience of the immaculate Holy Imams (a.s). This historical statement of Imam Reza (a.s) implied the presentation and assertion of the Imamate of His Holiness.
source:english.almaaref
