Imam (A) was the eldest son of Imam Husain (A). His mother was the Persian princess Bibi Shahr Banu (A), daughter of King Yazdjard II, the last pre-Islamic ruler of Iran.

He spent the first two years of his life under the care of his grandfather Imam Ali (A), and the next twelve years under the guardianship of his uncle Imam Hasan (A). In 61 A.H. he was present in Karbala, where his father, relatives and the companions of his father were mercilessly killed by the forces of Yazid. At the time, he was too ill to fight and was thus preserved by Allah to continue the line of Imamat.

Imam (A) lived 34 years after his father and all his life was passed in prayers and Du'as to Allah and in the remembrance of the tragedy of Karbala. His habit of frequent prostration in Sajdah caused him to be popularly known as Sajjad. He was also called 'Abid.

In his time, no one could equal the piety and awareness of Allah that he possessed. He was so mindful of Allah that whenever he sat for Wudhu, the colour of his face would change and when he stood for Namaaz his body would be seen trembling.

When he was asked why he became like this, he replied, "Do you not know before Whom I stand in prayers, and with Whom I talk?"

Imam (A) had a habit of going out at night with bags of money, food and even firewood. When he reached the houses of the poor and needy, he would distribute what he had without revealing his identity. It was only after his death that the people found out that their helper was actually Imam (A) himself.

Imam (A) was part of the caravan of captives that was led from Karbala to Kufa and then to Sham after the martyrdom of Imam Husain (A) and his companions.

The cruel army of Yazid chained the hands and legs of Imam (A) and made him wear an iron neckband with spikes facing inwards. The chains used to heat up in the hot desert and burn his flesh to the bone. These wounds continued to give him discomfort for the rest of his life.

In Sham, Imam (A) and the ladies and children of the party of Imam Husain (A) were imprisoned in very harsh conditions. Yazid once called Imam (A) and asked him to speak. Imam (A) gave such a powerful lecture that the feelings of the people began to be swayed towards him. Yazid was alarmed at this and ordered that Adhaan be recited so that Imam's (A) words would be cut off. At this, Imam (A) commented that he was the grandson of the same Muhammad (S) whose name they were reciting in Adhaan.

Due to the pressure of public opinion, Yazid decided to free his prisoners and let them return to Madina. But after his return, Imam (A) was again chained and sent to Sham on the order of the Bani Umayyah Caliph Abdul Malik. Later he was allowed to return to Madina.

After his return to Madina he retired from public life and was only in contact with some of the Shia who learnt from him and taught others.

Once when the Bani Umayyah Caliph, Waleed bin Abdul Malik, came for Haj, he could not get near and kiss the Black Stone (Hajare Aswad) because of the crowd of people. While he was sitting waiting for the rush to die down, he saw Imam (A) enter the Haraam and go straight towards the Black Stone. The crowds parted for him and he managed to kiss the blessed stone quite easily. Waleed was annoyed by this and asked who this man was, although he had recognised Imam (A).

A Shia poet, Farazdak, who was standing nearby, heard him and was irritated by the petty remark of Waleed. In reply to Waleed's question he composed a powerful and moving poem in praise of Imam (A). This poem exists today and is considered to be one of the masterpieces of Arabic literature.

Imam (A) was prevented by the government to preach openly so he used Du'as to guide the people. His Du'as contained a wealth of teaching and wisdom and many of them exist today. His most famous work is the book of 57 Du'as known as Sahifae Kaamilah.

Imam (A) was poisoned by Waleed bin Abdul Malik in 95 A.H. and is buried in Jannatul Baqee in Madina next to Imam Hasan (A).