He is the eighth Imam of the Imams of Ahl Al-Bayt (peace be upon them) known by Ar-Redha, his nickname is Abu al-Hassan. He was born in Medina on Friday the eleventh of Dhu Al-Qi'dah in the year 148 AH. He grew up in the lap of his father Imam Musa Al-Kadhem (peace be upon him), and was famous as he is one of the beacons of the nation, a pillar of the prophecy house known by the knowledge, sciences, generosity and courage...
Imam Ar-Redha (peace be upon him) became the Imam after the martyrdom of his father Imam Musa Al-Kadhem (peace be upon him) in the prison of Baghdad in the year 183, and he was then 35 years old, and his Imamate lasted for twenty years, ten years in the era of Harum Al-Abbasi, five years in the era of Caliphate of Mohammed Al-Amin and five years in the era of Ma'mun Al-Abbasi.
The life of Imam Ar-Redha (peace be upon him) represents an episode of the third stage in the life of Imams of Ahl Al-Bayt (peace be upon them), which is an expansionary phase within the ordinary populations, which reached in the era of his Imamate a greatest amplitude in its thesis of true Islam.
Imam Ar-Redha (peace be upon him) witnessed during his life many revolutions and uprisings against the Abbasids in all the Islamic World, from Kufa, Basra, Medina, Mecca and Yemen... And even in Baghdad that was their capital, there was revolutionary movements that threatened their rule, especially at the beginning of the Caliphate of Ma'mun, which pushed him to ask Imam Ar-Redha (peace be upon him) to calm them down, as he knew all of the leaders of the uprisings respected the Imam and would not refuse to listen to his advice.
Al-Ma'mun then obliged the Imam Ar-Redha (peace be upon him) to accept the offer of being his heir- apparent to succeed him after Mamun’s death, as a prelude to silence the revolutions and the unrest that are sweeping the corners of the unjust Abbasid state. And although the Imam (peace be upon him) refused it as he (peace be upon him) knows that he will be martyred before the death of Ma'mun. So Al-Ma'mun brought forcibly Imam Ar-Redha (peace be upon him) to Marw to be under his observation and to narrow his moves. That is why Imam Ar-Redha (peace be upon him) was not accompanied by any of his family members in this journey to show that it is not a normal trip but it is in fact a forced exile.
Ar-Rayyan Ibn Al-Salt asked Imam Ar-Redha (peace be upon him) about the reason for accepting the offer of being the heir- apparent of Mamun? Imam (peace be upon him) replied: "God knows that I am not satisfied with this, but I was at the crossroads of two roads, either I accept being the heir- apparent or being killed, so I accepted it."
Imam Ar-Redha (peace be upon him) went out of the Medina on the twenty-fifth of Dhu Al-Qi'dah in 201 AH and he arrived to "Marw" on the tenth of Dhu Al-Hijjah in the same year. He was welcomed by the noble personalities and the people from all the places he went through during his journey.
Throughout his long journey, the Holy Imam (peace be upon him) was cordially received by the people living in those cities and villages on the route. When His Holiness arrived in Nishapur he narrated a Hadith Qudsi before an estimated crowd of 120,000 which also included thousands of distinguished scholars and traditionists. This historical and the most famous Hadith Qudsi in known as "Silsilah Ad-Dahabyah [The golden chain]". Imam Ar-Redha (peace be upon him) confirmed that worshipping God will be counted as a perfect procedure when it is based on the obedience of the Immaculate Holy Imams (peace be upon them).
Wherever he stopped, during his journey towards Marv, he caused for many blessings upon the people. At one point on his way, he entered the city of Nishapur. A large crowd of people gathered to welcome his entrance. Meanwhile two learned men who had recorded many prophetic traditions came with scholars of Hadith, took the halter, and said: "You, the great Imam and you, the son of great Imams, for the sake of your innocent fathers and your great grandfathers, show us your shining face and narrate us a tradition from your fathers and your great grandfather, the messenger of Allah, to be as a reminder for us".
Imam ordered to stop and the people obeyed. Once they saw his face, they became so happy that some of them start crying and some who were close to him kissed his carriage. A big clamor was made throughout the city so, the elders of the city wanted people to be quiet so they could hear a tradition from Imam Ar-Redha (peace be upon him).
After a while the crowd got silent and Imam dictated this tradition word by word from his honored father which was narrated from his pure grandfathers from Imam Ali Ibn Abi Taleb and from the messenger of Allah (prayers and Allah's peace be upon him and his holy Household) and from Gabriel and from Almighty Allah that: "The word of La Ilaha Illa al-Allah is my fortress (then whoever says this has entered my fortress) and whoever enters my fortress will be saved from my punishment". Imam paused for a while and then said, "But on some conditions and I am one of its conditions."