Once when our 8th Imam, Imam Raza (as) was travelling through a town called Nishapur, the people of the town asked Imam Raza (as) to tell them a hadith from the Holy Prophet Muhammad (saw).
Imam Raza (as) told them the following hadith:
"My father Musa al-Kadhim (as) told me,
from his father Jafar Sadiq (as),
from his father Muhammad al-Baqir (as),
from his father Ali Zainul Abideen (as),
from his father the martyr of Kerbala (Hussain) (as),
from his father Ali ibn Abu Talib (as),
from the Holy Prophet Muhammad (saw).
from Angel Jibrail (as),
from Almighty Allah:
"The Kalima of 'La ilaha illallah' is My fort, and whosoever says it will enter My fort, and whosoever enters My fort is safe from My punishment."
This hadith is known as the Golden chain hadith. This is because each member of the chain was a Masoom (infallible). The people of Nishapur began reciting the Kalima and thought that His Holiness talk was over, but to their amazement the Holy Imam Raza (as) 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".
Source: Chennai Shia Youth Association
source : sibtayn