Shia’s fourth Imam is named Ali. He is the son of Hussain-ibn-Ali (Peace Be Upon Him), Shia’s third Imam. He was given the epithet “Sajjad”, meaning constantly praying, and “Zein-al-Abedin”, meaning the adornment of worshippers. Imam Sajjad was born in 38 AH(Lunar Calendar) corresponding to 659 AD(Georgian Calendar) his mother, Shahrbanoo, came from an Iranian clan.
Imam Zein-al-Abedin was present in the ،Tragedy of Karbala along with his father and his family, but by the will of Allah, he was very ill during the war of Karbala and could not fight in that Jihad. Although he was desperate to take part in the war, His magnanimous father did not allow him to do so. So that by the will of Allah, the earth shall not be devoid of his “Hojjah”. In the Tragedy of Karbala, where Imam Hussain, his brother ,Abalfazl-al-Abbas, and several of Imam Sajjad’s cousins were martyred, By the order of “Allah” and according to Prophet Muhammad ‘s will; “Imamate” (leadership of the people), after Imam Hussain, was bestowed upon his son Ali-ibn-al-Hussain, and thus Imam Hussain delivered his son with all the necessary devine secretes, before his martyrdom.
Imam Sajjad’s illness didn’t last long and after that, being a powerful young man of about 24, he took over the responsibility of leading the nation.

Imam Sajjad’s era and the carrying out of his mission
Imam Sajjad’s Imamate period was abound with hardship and this time went as the magnanimous Imam and his followers suffered immense oppressions, because of the numerous obstacles in the way of his leadership and guidance of the society. On the one hand those who unjustly reigned over the Islamic society in the government where the very ones who had martyred Imam Hussain and his family in the most unimaginably brutal and ruthless way. on the other hand those ostensibly Muslim rulers, “Khalifs”, in reality were the most corrupt and oppressive people ever. because of the plot contrived and spread by the government, ignorance and aberration was rampant in the society. Throughout that excruciatingly tough time, Imam Zein-al-Abedin(PBUH) was in pursuit of a number of goals in line with accomplishing his divine Imamate mission and fulfilling his sacred responsibility. First and foremost, he attempted to keep the memory of the tragedy of “Ashura” alive by citing the events and facts of that day. Imam carried out this important deed through his fiery orations. A good example of this is his famous oration in Yazid-ibn-Muawiyah’s court when Imam Sajjad and his family were taken captive. Yazid, was then the ruler of the Islamic states. There in the presence of Yazid and his throng of supporters, Ali-ibn-al-Hussain with all bravery and unbelievable soul power delivered an enlightening speech which made the audience cry and come to a realization of truth.
In line with such enlightening deeds, whenever he wanted to drink water or eat food, Zein-al-Abedin would commemorate his father and other martyrs of Karbala, who had been killed as they were thirsty.
Imam’s second goal was to prevent the elimination of the truths and principles of the true Islam at the hands of tyrant rulers and their proponents or because of ignorance or ill intention of some people.
His next goal was to elucidate the principle of “Imamate” and “Vilayah” to the people, so that the society would truly understand what leadership of the Islamic society means, what responsibilities the prophet’s successor has, and who Allah’s true Khalifa, people’s Imam and leader on earth is. Imam Sajjad (PBUH) corrected the concept of “Imamate” in people’s minds. He announced to truth seekers that he was the rightful Imam and not the ruler of the day who by deception was misleading the society.

Considering the repression and severe dread of government among people, Imam Zein-al-Abedin managed these goals through some intelligent schemes.

Stating pray and devotions was among the most important means used by him to guide people. He gave insight to audiences using prays, restoring the Shia party by patience and expectancy culture policy.

A set of most sophisticated and magnificent prays of Imam Sajjad is collected in “Al-Sahifa al-Sajjadiyya” book, known as “Zabur Ale Muhammad” which presents a collection of scientific, ethical and Islamic sciences in form of words, prays and devotions.

Imam Sajjad (bless upon him) had to devise a plan to revive the true Islam in his lonely exile. According to authentic historical references, while he had not more than 20 companions in Medina, Imam Sajjad trained many students to deliver the pure Islamic sciences to people and eliminate ignorance in the society.

Through this way, for restoration of prophet missed sunna, he started training slaves. He named his salves, children and called them “My Son”. With this action, he wanted to intimate that there is no difference between a free Muslim and a slave in his opinion. Imam Zein-al-Abedin never punished his slaves but he put down their mistakes and gathered them at the end of Ramadan, reading it for them and asking them to leave those behaviors. He asked them to ask God forgive him as he has forgiven them. Then he gave them a gift and manumitted them for sake of God, turning them into messengers for spreading Islamic science and ethics. Moreover, Imam granted the needed facility for a good and independent life to them. By this method, an army of more then 50 thousands manumitted men and women was prepared who were in Imam Sajjad’s power. Some of these manumitted people whom were trained in Imam’s school turned into prominent scientists like Hasan bin Saeed Ahvazi, Husain bin Saeed Ahvazi, Ahmad bin Husain bin Saeed and Shuaib.

Like other Ahl al-Bayts, Ali bin Husain was generous, forgiver and helpful to poor people and respected them by sharing meals. For instance, he carried food and breads at nights personally, delivering it to poor people and orphans anonymously.

Imam Sajjad martyrdom (God bless him)
As time went on, the Omavi system figured out the confrontation methods of Imam Sajjad and concluded that having Imam alive in the society is a threat to their government. Moreover, Abdulmalek, hisham -the ruler at the time- , Valid and even some elites of Umayyad dynasty were envious of him since people admired Imam due to his wisdom and intelligence. Moreover, they decided to murder him because of his revealing about Ashura and the assumption that Imam was planning to rise against the government. They murdered the 4th Imam of Shias by poison at the age of 57, on 25 Muharram 95 Hijri, in AD 713 after 35 years of imamate.
His holy shrine is located in Medina alongside his uncle Imam hasan, Imam Bagher and Imam Sadegh’s shrine in Jannat al-baqi.