After the martyrdom of his father, Imam Hassan's son Abdullah lived with his holy uncle, Imam Hussein (A.S) and loved him very much. Imam Hussein too had a great affection for his young nephew. "'Abdullah went to Karbala with his uncle and saw everything that happened there.
He saw his young brothers and cousins putting on their suits of armor and, with the cry of "Allahu akbar' and their swords whirling, rushing off to the battlefield. He saw them fighting battle with the enemies of religion and of the Qur'an, the disbelievers and hypocrites, and saw them killing them and being killed. He saw them drowned in their holy blood, giving life and strength to Islam with their martyrdom. When their bodies were brought to the special tent for the martyrs, Abdullah would go and weep over their bodies. He wanted to go to the battlefield and fight with the oppressors and defend Islam and its holy leader, lmam Hussein (A.S), but he was very young and they wouldn't give him permission.
It was the day of 'Ashura' and all his friends, brothers and all of Imam Hussein's valiant troops had been martyred. and 'Abdullah had witnessed the martyrdom of them all.
Before they rushed off to the battlefield, he had heard everyone of the martyrs conveying their final goodbyes, and promising never to desert their leader and Imam or leave him on his own.
The last of Imam Hussein's men had bravely given his life. He had been martyred. Now Imam Hussein himself left for the battlefield. Abdullah was standing near the martyrs' tent, watching his uncle from a distance. An hour later, he couldn't see his uncle any more. Without thinking he instinctively ran towards the battlefield. His aunt, Zeinab, wanted to stop him, but couldn't. Abdullah wanted to find his uncle and defend him. Finally, he found him soaked in his own blood. Confused and dumbfounded, he stood staring at the bleeding face of his dear uncle. Imam Hussein opened his eyes and both of them saw each other.
Suddenly a sword was raised to deliver the final blow to Imam Hussein (A.S). Abdullah saw the flash of the sword and raised his head. "Do you want to kill my uncle you filthy traitor! he cried!" And immediately shielded his uncle's bleeding body with his arm.
The sword fell. It cut off Abdullah's arm, and the body of that brave and selfless youth fell on the chest of Imam Hussein (A.S). He attained martyrdom then and there giving the message of jihad and freedom to the youth of all times. With his last breaths, Imam Hussein (A.S) said to him, "My dear child, martyrdom is our honor. Your father Imam Hassan and your grandfather, the Holy Prophet, are waiting for you in Paradise, and we are going to them together."
Source:
The Children's Book On Islam
By: AYATULLAH IBRAHIM AMINI
BOOK TWO
P. 98 - 100
source : www.tebyan.net