Following is the text of a speech by Leader of the Islamic Revolution Ayatollah Seyed Ali Khamenei deleivred back in April 2016 about the life of Imam Hadi (AS), according to khamenei.ir:
In the battle between Imam Hadi (AS) and the caliphs of his time, the person who achieved victory inwardly and outwardly was Imam Hadi (AS). This should be reflected in all of our statements.
During the imamate of that great Imam, six caliphs came and perished one after the other. The last one was al-Mu'taz who martyred Imam Hadi (AS) and who died shortly after. These caliphs died in humiliation. One was killed by his son and another was killed by his nephew. The rest of Abbasid caliphs were destroyed in such a way. Contrary to these caliphs, Shia Muslims prevailed. During the time of Hazrat Hadi (AS) and Hazrat Asgari (AS) Shia Islam expanded and became stronger despite the harsh measures adopted by Abbasid caliphs.
Hazrat Hadi (AS) lived for 42 years. Out of these 42 years, he spent 20 years in Samarra. He had a farm there and he used to work and live in this city. At that time, Samarra was like a military camp which had been built by al-Mu'taz to keep his Turkish slaves - these people should not be mistaken with our Turks in Azerbaijan and other areas in Iran - who were close to him and who had been brought from Turkistan, Samarkand, Mongolia and East Asia.
Because these Turks had just converted to Islam, they did not know the Imams (AS) and believers and they did not know much about Islam. For this reason, they used to bother the people and they came into conflict with Arabs - that is to say, the people of Bagdad.
In Samarra, a large number of Shia personalities gathered and Imam Hadi (AS) managed to lead them and deliver the message of imamate, by writing letters and other such things, to the entire world of Islam. This was done with the help of these Shia personalities. It was these Shia Muslims who managed to promote the Shia networks which exist today in Qom, Khorasan, Rey, Madina, Yemen, certain remote areas and many other cities throughout the world. They managed to expand Shia Islam on a daily basis.
Imam Hadi (AS) did all of these things while he was threatened by the sharp and blood-thirsty swords of these six caliphs. He made such moves despite their wishes. There is a well-known hadith about the demise of Hazrat Hadi (AS) which makes it clear that a large number of Shia Muslims had gathered at his funeral in Samarra. Abbasid caliphs did not know them because if they had, they would have killed all of them. But because these Shia Muslims had established a strong network, Abbasid caliphs could not have access to them.
One day of the efforts of our great Imams (AS) would exert years of influence. One day of the auspicious lives of these great Imams (AS) would exert years of influence in society, like a group of people who work for years to achieve something. These great Imams (AS) preserved religion. Had it not been for the Imams (AS), Islam - which was under the control of al-Mutawakkil, al-Mu'taz, al-Mu'tassim and al-Ma'mun and which was led by corrupt scholars like Yahyah ibn Aktham - would not have prevailed. Although such scholars were knowledgeable, they were notoriously corrupt and deviant. Had it not been for the Imams (AS), Islam would have been destroyed soon. Not only did the great diligence and efforts of the Imams (AS) preserve Shia Islam, but it also preserved the Holy Quran, Islam and religious teachings. These are the characteristics of pure and sincere servants of God and His saints.
If Islam had not had people who were prepared to protect it, it could not have been revived after the passage of 1,200, 1,300 years with the emergence of Islamic Awakening. Had it not been for these people, it would have been destroyed little by little. After the demise of the Holy Prophet (PBUH), if Islam had not had certain people to inculcate the great Islamic teachings in the minds of people throughout human and Islamic history, it would have been destroyed and nothing would have remained of it. Even if it had survived, nothing would have remained of Islamic teachings and it would have become like Christianity and Judaism in which almost nothing has remained of religious teachings.
The fact that the Holy Quran and the hadiths which were narrated by the Holy Prophet (PBUH) are intact, that all Islamic obligations and teachings have been preserved and that Islamic teachings have managed to show themselves after the passage of thousand years shows that this was not done by natural forces. This was done by supernatural forces and it was achieved with diligence. Of course, one may be beaten, imprisoned and killed on this great path, but this was nothing for our great Imams (AS).
During the 250-year imamate of our Imams (AS) - from the demise of the Holy Prophet (greetings be upon him and his household) to the demise of Hazrat Asgari (AS) - the Imams (AS) endured great sufferings. They were murdered and oppressed. This requires that we cry for them. The oppression against them has made hearts and souls pay attention to them. But despite this oppression, the oppressed Imams (AS) achieved victory, both during their own era and in general throughout history.