However, according to the Shia view, when Al-Ma'mun saw that the Imam gained even more popularity, he decided to correct his mistake by poisoning him.The Imam was buried in a village in Khorasan, which afterwards gained the name Mashhad, meaning the place of martyrdom.On the eleventh of Dhu al-Qi'dah, 148 AH (December 29, 765 CE), a son was born in the house of Imam Musa al-Kadhim (the seventh Imam of Twelver Shia Islam) in Medina.
His mother, Najmah, was also a distinguished and pious lady.
It is said that the boy al-Ridha required a great deal of milk, so that when his mother was asked whether her milk was sufficient, she answered, "it is not because my milk is not sufficient, but he wants it all the time, and consequently I am falling short in my prayers." Yazid ibn Salit has also related a similar narration from the seventh Imam when he met him on his way to Mecca: "Ali, whose name is the same as the First and the forth Imam, is the Imam after me." Said the Imam.
However, due to the extreme choking atmosphere and pressure prevailed in the period of Musa al-Kazim, he added, "What I said must remain (restricted) up to you and do not reproduce it to anybody unless you know he is one of our friends and companions." According to Donaldson he was twenty or twenty-five years old when he succeeded his father as Imam in Medina, and it was about eighteen years later, when the Caliph Al-Ma'mun "undertook to ingratiate himself with the numerous Shia parties by designating Ali ar-Ridha as his successor to the Caliphate." After the death of Harun al-Rashid in 809, Harun's two sons began fighting for control of the Abbasid Empire.
One son, Al-Amin, had an Arab mother and thus had the support of Arabs, while his half-brother Al-Ma'mun had a Persian mother and the support of Persia.
The Shia of al-Ma'mun's era, like the Shia of today, who made a large population of al-Ma'mun's Iran, regarded the Imams as their leaders who must be obeyed in all aspects of life, spiritual and terrestrial, as they believed in them as the real caliphs of the Islamic Prophet, Muhammad.
The Abbasids, like the Umayyads before them, realized this as a big threat to their own caliphate, since the Shias saw them as usurpers of al-Ma'mun which was far from the sacred status of their Imams.
Allamah Tabatabaei writes in his book Shi'ite Islam, that in order to quiet the many Shia rebellions around his government, al-Ma'mun summoned Imam al-Ridha to Khorasan and wanted to offer him the role of Crown Prince to prevent the Shias and relatives of al-Ridha from rebelling against the government, seeing as they would then be fighting their own Imam; secondly, to cause the people to lose their spiritual belief and inner attachment to the Imams, because the Imam would be associated with the corrupt government of al-Ma'mun.
or in Persia(Iran) as Imam Reza (Persian: امام رضا), was a descendant of the Prophet Muhammad and the eighth Shia Imam after his father Musa al-Kadhim and before his son Muhammad al-Jawad.
He was an Imam of knowledge according to the Zaydi (Fiver) Shia school and Sufis.
He lived in a period when Abbasid caliphs were facing numerous difficulties, the most important of which was Shia revolts.
The Caliph Al-Ma'mun sought out a remedy for this problem by appointing Al-Ridha as his successor, through whom he could be involved in worldly affairs.