How did Imam Reza (as) expose the tyranny of Ma'moon while empty-handed?Ayatollah Khamenei answers:
In the Name of Allah, the Beneficent, the Merciful
I would like to congratulate all you dear brothers and sisters - who have participated in this meeting - all the dear people of Iran and all believers and Muslims throughout the world on the occasion of the auspicious birthday anniversary of Hazrat Ali ibn Musa ar-Ridha Thamen ul-Hujjaj (God's greetings be upon him).
Although the blessed lives of the Imams (a.s.) during the 250 years of their Imamate contain many outstanding and prominent points each of which requires careful analysis, attention, tafsir and reconsideration, the era of the eighth Imam (God's greetings be upon him) is one of the best eras in this regard.
The beginning of the eighth Imam's (God's greetings be upon him) Imamate coincided with the dictatorial rule of Harun al-Rashid. This happened after the martyrdom of Musa ibn Ja'far (a.s.) in prison. Anyone who showed the slightest disobedience to the wishes of the ruling system faced unrelenting pressures. It was in such circumstances that the eighth Imam (a.s.) achieved Imamate.
There is a narration which says, "One of the followers of the Imams (a.s.) said, This young person, the son of Musa ibn Ja'far, has accepted this responsibility. This is while blood trickles from Harun's sword'" [al-Kafi, Volume 8, page 257]. This narration says, "Blood trickles from Harun's sword". It was in such circumstances that Imam Ridha (a.s.) became an Imam. In such difficult circumstances, this great personality managed to develop among the Muslim society of those days the bright line of the Holy Prophet's (s.w.a.) tradition and Quranic and Islamic teachings.
He managed to help hearts get close to the school of the Holy Prophet's (s.w.a.) household. Then it was Ma'mun's turn and the story of his attempt to bring that great personality from Madina to Marv and Khorasan. At that time, Marv was the capital of Abbasid rule. They had changed the capital from Baghdad to Marv. Of course, later on, they made Baghdad the capital again. Baghdad was the center of Abbasid policy. The motivation behind the decision of Ma'mun and his ruling system to transfer the eighth Imam (a.s.) to Marv requires a long discussion.
Ma'mun had made a calculation which was purely political. His policy was to strengthen the bases of his power and to weaken the movement of the Holy Prophet's (s.w.a.) household (God's greetings be upon them) and what they wanted to do. In the face of Mamun's political and shrewd move, the eighth Imam (a.s.) drew up and implemented a divinely intelligent plan. This plan not only foiled the plot and requests of the ruling system but it also led to the development of Quranic teachings and the ideas and thoughts of the Holy Prophet's (s.w.a.) household throughout the world of Islam.
With a great movement, with reliance on Allah the Exalted, with divine wisdom and acumen and with an efficient and wilayati outlook, the eighth Imam (God's greetings be upon him) managed to foil this hostile plot of the dictatorial and oppressive ruling system and to use it to the advantage of the truth. This is an outstanding chapter of the history of the Imams (a.s.).
Ayatollah Khamenei's Speech in Meeting with Hajj Officials; September 07, 2014