In order to have his last decision put into effect, Ma'mun asked Imam ar-Reza to come to Marw from Medina. This was the longest journey undertaken by any of the Shi‘a Imams: from Medina (north-west of Arabia) to Marw (in Turkmenistan, north of the Afghan border). The Imam passed through southern Iraq, into sourthern Persia on to the famous city of Neshapur and further north into Turkmenistan.
This journey itself availed an opportunity for the Muslim populace to see the Shi‘a Imam (a descendant of the Holy Prophet) in person and hear his words of wisdom. While the Imam was about to leave Nishapur, the scholars of the city took hold of his camel's reign and insisted upon him to narrate from his forefathers: The Imam obliged as follows: My father, Musa bin Ja‘far, narrated to me from his father, Ja‘far bin Muhammad, who narrated from his father, Muhammad bin ‘Ali, who narrated from his father, ‘Ali ibn al-Husayn, who narrated from his father, al-Husayn bin ‘Ali, who narrated from his father, ‘Ali bin Abi Tâlib, who said, I heard the Prophet (s.a.w.) saying, "I heard Jibrail saying, ‘The Almighty Allâh said, "I surely am the God besides whom there is no god, so worship Me. Whoever comes with the testimony of tawhid sincerely, he has surely entered My castle; and whoever enters My castle, he shall be protected from My chastisement."'"
Then the Imam added that this salvation is guaranteed "with its conditions; and I am one of its conditions." That is, together with tawhid, one must also believe in other fundamentals of Islam like nubuwwa and imamat in order to gain salvation in the hereafter. Because of its excellent chain of narrators, this hadith is known as "hadith silsilatu 'dh-dhabab - hadith with the golden chain [of narrators]."
source : www.tebyan.net
