Imam Zainul Abideen (peace be upon him) was the only son of Imam Hussain to survive, for his other two brothers Ali Akbar and Ali Asghar, who was a suckling baby, were martyred during the event of Karbala. The Imam had also accompanied his father on the journey that terminated fatally in Karbala, but because of severe illness and the inability to carry arms or participate in fighting, he was prevented from taking part in the holy war and being martyred.
Islam: Faith, Practice, & History by Sayyid Muhammad Rizvi
On the 5th of Shaaban, 36 AH in Medina, Imam Ali ibn al-Hussain was born to the third Imam, Imam Hussain (peace be upon him). Throughout his life, Imam Ali ibn al-Hussain became known as Zainul Abideen – the "prince of the worshipers" and Sajjad – the "one who prostrates most". Imam Sajjad was two years old when the Prince of Believers, Imam Ali (peace be upon him) was martyred, and he also lived through the life of his uncle Imam Hasan (peace be upon him). As mentioned above, Imam Zainul Abideen witnessed and survived to tell the saga of Karbala.
After the day of Ashura, the enemies attempted to take the Ahlul Bayt (peace be upon them) as captives to Kufa and from there to Damascus with the intent of humiliating them and presenting them as an example for any potential opposition to the tyrant Yazid's rule. However, with Lady Zainab and Imam Sajjad's leadership, the journey in captivity became an opportunity for the Ahlul Bayt to wake the people up to the true realities which Imam Hussain fought for.
Even in the tyrant Yazid's court, Imam Sajjad addressed the people after a speaker tried to stir up the crowd against Ahlul Bayt, saying:
"Those who know me, they know me. And those who do not know, then listen:
"I am the son of Mecca and Mina; I am the son of Zamzam and Safa; I am the son of the noble one who placed the black stone in the Ka'bah; I am the son of the one who put on the Ihram and did Tawaf; I am the son of the one who was taken from Masjidul Haram to Masjidul Aqsa [in Me'raj]; I am the son of one on whom Allah sent revelations;
"I am the son of Hussain, who was killed in Karbala; I am the son of Muhammad al-Mustafa; I am the son of Fatima Zahra; I am the son of Khadija al-Kubra;
"I am the son of the one who was killed and left in a pool of his own blood; I am the son of the one who was left without a shroud and without burial; I am the son of the one who was killed thirsty."
Upon hearing these words and the likes of them, the masses were brought to tears. Due to public pressure, Yazid was eventually forced to publicly disown the actions of his own soldiers. Most importantly, people were becoming more aware of the atrocities that had been committed.
When the Ahlul Bayt were allowed to return to Madina, Imam Zainul Abideen refrained from any political activity and dedicated his life to further the knowledge of his followers in religious and spiritual matters. One result of Imam Sajjad's work is laying the foundation for his son Imam Muhammad al-Baqir and grandson Imam Ja'far as-Sadiq (peace be upon them) to extensively spread the teachings of the Ahlul Bayt in various fields of knowledge.
Another treasure that Imam Sajjad left for the generations is a compilation of supplications and prayers, known as al-Sahifa al-Kamilah as-Sajjadiya. Many find that the words of Imam Sajjad's supplications extraordinarily express the feelings a servant may have toward the Lord of the Worlds. One group of these supplications is known as The Fifteen Whispered Prayers, and these specific prayers can be regarded as remedies for the different states one's heart may be in. For example, if one is feeling down and frightened, that person may feel comforted by reading part of the Whispered Prayer of The Fearful:
"My God, what thinks Thou? Wilt Thou chastise me after my faith in Thee, drive me far away after my love for Thee, deprive me while I hope for Thy mercy and forgiveness, forsake me while I seek sanctuary in Thy pardon? How could Thy generous face disappoint me?! Would that I knew – did my mother bear me for wretchedness? Did she nurture me for suffering? Would then that she had not borne me and had not nurtured me?! Would that I had knowledge – hast Thou appointed me one of the people of felicity? Hast Thou singled me out for Thy nearness and neighborhood? Then would my eyes be gladdened, and in that my soul will reach serenity."
If one is feeling like a lover, it may be a good idea to read part of the Whispered Prayer of the Lovers:
"O Utmost Limit of the hopes of the lovers! I ask from Thee love for Thee, love for those who love Thee, love for every work which will join me to Thy nearness, and that Thou makes Thyself more beloved to me than anything other than Thee and makes my love for Thee lead to Thy good pleasure, and my yearning for Thee protect against disobeying Thee!"
One finds that through the different prayers and supplications, Imam Sajjad teaches us how to converse with the Lord Most High and become more ideal individuals in the process.
Despite the fact that the Imam did not get involve in public politics, the government still kept a close watch on him. The popularity of the Imam angered the rulers of his time, and they could not bear to see his circle of influence grow any further. The holy Imam was poisoned by Walid ibn Abdul Malik and was martyred on the 25th of Muharram, 95 AH. He is buried in the Jannat al-Baqi cemetery in Medina along with other members of the Ahlul Bayt.