Imam Ali ibn Musa ar-Ridha (peace be upon him) was born on 11 Dhul Qadah, 148 AH, in Medina. The Imam lived through most of his father's struggles under the corrupt Abbasid tyrant Harun ar-Rasheed. After Imam Musa al-Kadhim (peace be upon him) was martyred in 183 AH, Imam Ali ar-Ridha was active in helping the needy and educating the people of Medina.
The number of followers of Ahlul Bayt (peace be upon them) increased in secret under Harun's reign. When Harun died in 193 AH, political turmoil overcame the Muslim world. The two sons of Harun - al-Amin in Baghdad, Iraq, and Mamoon in Khorasan, Iran - fought for control of their father's throne, while some anti-government movements formed in various parts of the Muslim world. It became clear soon enough, however, that Mamoon was militarily superior. Al-Amin was killed after only about four years.
Mamoon was worried that Imam Ali ar-Ridha and his followers could form a threat to his government, so he insisted that the Imam come to his palace in Khorasan, away from his supporters in Medina. From one aspect, Mamoon wanted to keep the Imam away from his followers. From another aspect, he wanted to gain credibility with the presence of the Imam in his capital. The Imam knew that his supporters were not yet spiritually prepared to sacrifice their worldly lives to topple the Abbasid government. So the Imam responded to Mamoon's call, saving Medina from further problems.
Along the way to Khorasan, the Imam was greeted by large numbers of people, which surprised Mamoon and his entourage. At various stops, the Imam would give words of wisdom about Allah, Islam, and the Ahlul Bayt (peace be upon them). In order to use Imam ar-Ridha to his advantage, Mamoon demanded that the Imam accept a symbolic position called Wilayat al-Ahd. This was basically a promise that the Imam would become the next caliph. The Imam refused, but then Mamoon threatened him by saying, "Indeed, Umar (the second caliph) made the Shura with six people. One of them was your grandfather (i.e. Imam Ali), and he (Umar) said: 'Whoever violates it, then cut off his head!' It is imperative to accept it." In other words, just like Imam Ali ibn Abu Talib (peace be upon him) had no choice but to become a member of the infamous six-member Shura, similarly Imam ar-Ridha had no choice but to accept the Wilayat al-Ahd.
The Imam responded in a very precise statement - speaking the language of politics while holding firm on principles - that he would accept as long as he did not have to "command or forbid, appoint or remove, speak between two groups in a judgment, or change anything that is already standing on its roots." In other words, the Imam's conditions made sure that the Imam took no part in Mamoon's government! Mamoon took the response and advertised that the Imam had accepted Wilayat al-Ahd, but the followers of the Imam found out what had really happened. However, Mamoon did not realize that when he thought he was winning over the followers of Ahul Bayt to his side, he was really only making the Imam more popular, even in the Abbasid circles.
Mamoon's palace became a headquarters for scholarly debates, and Imam Ali ar-Ridha was always the fountain of knowledge that made truth clear from falsehood. In one of the debates with Christian scholars, the Imam reached a point where he said, "O Christian, by Allah, we believe in the Jesus (peace be upon him) that believed in Muhammad (peace be upon him and his progeny), and we don't criticize your Jesus except in the weakness and lack of his fasting and prayer."
The Christian scholar Jathleeq responded, "By Allah, you have corrupted your knowledge and weakened your issue ... and I thought that you were the most knowledgeable of the Muslims!" The Imam said, "And how is that?" The Christian replied, "You said that 'your Jesus was weak and lacking in his fasting and prayer,' when Jesus (almost) never broke his fast on any day, nor did he sleep throughout the whole night, but rather he fasted and stayed up in worship at night." The Imam replied, implicitly clarifying his initial statement, "So, (if you say Jesus is God,) whom did he fast for and pray to?"
Mamoon's diabolical plans did not work as he wished. Imam ar-Ridha was loved by the people, the scholars were amazed by his knowledge, and Mamoon could not handle it anymore. Mamoon poisoned the Imam, and the Imam was martyred in the end of Safar 203 AH. He was buried in present-day Mash'had, Iran, where his shrine today is visited by millions of followers each year.
by: Ali Jamaleddine