Imam 'Ali b. Musa al-Rida (a) (Arabic: علي بن موسی الرضا) (b. 148/766 – d. 203/818) is the eighth Imam of Twelver Shia. His Kunya was Abū l-Ḥasan (Arabic: أبو الحسن) and his most famous title was al-Riḍā (Arabic: الرضا). He (a) was Imam for 20 years. Imam al-Rida (a) was born in Medina and was martyred in Tus. The holy shrine of Imam al-Rida (a) is in Mashhad and every year millions of Muslims from different countries visit it.
Al-Ma'mun al-'Abbasi brought Imam al-Rida (a) to Khorasan by force and despite Imam's will made him crown prince. The route, al-Ma'mun chose for bringing Imam al-Rida (a) to Merv was specifically planned so that Imam (a) does not pass from Shi'a cities because he was afraid of Shi'a gathering around Imam al-Rida (a). He ordered not to pass Imam (a) from Kufa, instead they brought Imam (a) from Basra to Khuzestan and Fars to Neyshabur. The path as reported by Atlas of Shi'a is: Medina, Naqara, Nabaj, Hafr Abu Musa, Basra, Ahvaz, Behbahan, Estakhr, Abarquh, Dah shir (Farashah), Yazd, Kharaneq, Robat Posht Badam, Neyshabur, Qadamgah, Deh Sorkh, Tus, Sarakhs, Merv.
The most important and most documented event of this path happened in Neyshabur where Imam al-Rida (a) made a speech and said the famous hadith of Silsilat al-Dhahab.
After Imam (a) settled in Merv, al-Ma'mun sent an agent to his house and told Imam (a) that "I want to depose myself from Caliphate and leave it to you!", and asked Imam (a) about his opinion. Imam (a) seriously opposed his idea. So, al-Ma'mun asked him to accept to be the crown prince after him. Imam (a) again disagreed, then al-Ma'mun summoned Imam (a) to his house and in a session, where there was no one except him, Imam (a) and al-Fadl b. Sahl, and told Imam (a), "I want to leave Muslims' affairs to you and unburden myself from this responsibility and leave it to you." Read more...