In the time of Imam Reza (A.S.) Nishabur was a famous center of learning in Khorasan and was full of scholars. As the news of the Imam's (A.S.) arrival spread through Nishabur, tens of thousands of people from all walks of life, including scholars and scientists, gathered on the outskirts of the city to welcome the Prophet's noble descendant. The multitude jostled with each other to have a glimpse of the Imam's spiritual and radiant face, as the grandson of the Prophet entered the city of Nishabur in ordinary clothes but with a dignified appearance.

Two of the city's prominent 'ulema , Abu Zar;a and Muhammad bin Aslam Tusi, went near the camel on which the Imam was riding and after salutations, requested that he narrate on the chain of authority of his illustrious forbears so that they could learn it from his memorable self and keep alive the memory of his historical journey. It is said that about 24,000 scholars gathered around the camel with pen and paper to record the Imam's blessed words.

After a brief pause, Imam Reza (A.S.), narrated the famous tradition known ever as 'Hadith Silsilat az Zahab' or the 'Golden Chain of Authority' , saying: 'My father Imam Musa al Kazem (A.S.) told me that he heard from his fathr ImamJfar as Sadeq (A.S.) , who heard from his father Imam Muhammad al Baqer (A.S.) , who herad from his father Imam Ali ibn al Hussain (A.S.) , who heard from his father Imam Hussain ibn Ali (A.S.) , who heard from his father Imam Ali ibn Abi Taleb (A.S.) , who heard from Prophet Muhammad (S.A.W.A.) who heard from Almighty Allah, Who said: the testimony la ilaha ill-Allah (there is no god except Allah) is My impregnable fortress and whoever enter My fortress is safe from My wrath.

In fact, Imam Reza's (A.S.) saying was the same declaration of the principle of Tawheed(Monotheism or  the Oneness of God) which Prophet Muhammad (S.A.W.A) had proclaimed in Mecca for the frist time over two centuries ago.

The Imam stayed silent for a while then continued "But it (entering Alla's impregnable fortress) has certain condition and stipulation, and I am one of those conditions.

In other words, Imam Reza (A.S.), by emphasizing on this Hadith Qudsi, meant to stay that acceptance of the 'Oneness of God' and the leadership of Prophet Muhammad (S.A.W.A) and the infallible Imam of his Household, was the prime condition for being safe from Divine Wrath. In fact, the belief in Monotheism wiil only become complete with the acceptance of the leareship of the Prophet's infallible Household.

Imam Reza (A.S.) thereafter left Nishabur and proceeded towards Merv, passing through the place which is known to this day as Qadamgah . since it still bears the footprint of the Eighth Imam. From Dah Sorkh village, he arrive in Sanabad, where he stayed in Hamid bin Qahtaba's palace and saw Harun's grave . On entering  the dome, under which lay Harun;s remains, the Imam marked a spot with his blessed hand, saying: "I will be buried here, an Almighty Allah will make this place a site of pilgrimage for my shias (followers) and my friends. By Allah, whoever comes for my pilgrimage and recite salutations (Ziyarat) upon me, will be guaranteed divine mercy and forgiveness by virtube of the intercession of our family (Prophet's Household)."

After two days of stay, Imam Reza (A.S.) left Sanabad for Merv by way of Sarakhs.