Aun and Muhammad
Aun and Muhammad were the sons of Bibi Zainab, and they were quite young, aged ten (10) and nine (9) years respectively. They had learnt the art of fencing from their uncle, Abbas the brave.
When devotee after devotee fought and fell, in defense of the Holy Family, Aun and Muhammad felt that it was now their turn to go to the battlefield. They went to their mother Zainab (pbuh), to ask for her blessings. Aun and Muhammad assured their mother that they would fight with such bravery that whenever she thought of them, she would remember how brave they were. Zainab (pbuh) went to her brother to request him, and said: "Hussain, at the Battle of Siffin, Abbas was only ten (10) years old. When he saw someone trying to attack you, he rushed into the battle field and killed the man. Do you remember how proud our father Ali was? Today I too want to be proud of my sons. I want to see them go out there and defend Islam. Will you not allow me that privilege?"
Imam Hussain (pbuh) stood there in silence. He looked at his sister. He saw the disappointment on her face, and saw tears forming around her eyes. Then said: "My beloved sister you have never asked me for anything before, how can I say no to you now." He turned to Aun and Muhammad and said "Go my sons, be brave, I shall join you soon on your journey to the heavens." Bibi Zainab held them close and kissed them goodbye. The boys raised their hands and said "Fi Amaani-llah, mother!" Bibi Zainab replied, "Bismillah my sons. God be with you!"
The two boys rode out into the battlefield. They fought bravely. At one point 'Umar son of Saad' asked, "Who are these two youngsters? They fight like I have seen Ali son of Abu Talib fight." When he was told who they were he ordered his soldiers to give up single combats and surround and kill the boys. Aun and Muhammad were attacked from all sides.
Imam Hussain, Abbas and Qasim, stood by Zainab as she watched her sons fighting. Hardly a few minutes had passed when Aun fell from his horse and shouted for Imam Hussain. Just at that moment another cry was heard, this time from Muhammad. Abbas left Qasim with Zainab while he ran to the battlefield. Imam Hussain carried the body of Aun while Abbas carried Muhammad.
Imam Hussain (pbuh) walked to Zainab's tent. He found her in Sajdah praying, "Oh my God, I thank you for accepting my sacrifice. My heart is filled with pride because my two sons have given their lives for your religion."
Bibi Zainab came to the two bodies of her sons and addressing them said: "My dear children! Now I am pleased with you that, you have proved your worth and laid down your lives for Truth and pleased God and His Holy Prophet (pbuh)."
Imam Hussein(as)
Qasim son of Imam Hassan (as)
Qasim was the youngest son of Imam Hassan (pbuh), he was born in 47 Hijra, three (3) years before the martyrdom of his father. When Imam Hussain (pbuh) prepared to leave Madina in the month of Rajab 60 Hijra. Qasim's mother Farwa asked Imam Hussain to take her and Qasim with him. Imam Hussain (pbuh) agreed. Qasim, although only thirteen (13) years old, had, like his cousins Aun and Muhammad, learnt fencing from Abbas and Ali Akbar.
After Aun and Muhammad had fallen in the battlefield, Qasim came to Imam Hussain (pbuh) and begged for permission to go and fight. Twice Imam Hussain (pbuh) refused saying "Qasim you are young and your mother's only son." After much insistence, received the permission to leave for the battlefield, being very young, there was no armor that was fit for his years, nor a helmet nor shoes, nor arms. Imam Hussain (pbuh) tied Imam Hassan's turban (Amamah) on the head of Qasim and helped him mount his Horse. Qasim came to the battlefield. He was a very handsome boy. When the enemy saw him, they began to murmur, "How can we kill someone whose face is shining like moon?"
In a loud and a clear voice Qasim introduced himself and cried out a challenge for single combat. He killed several famous warriors who came forward. When 'Umar son of Saad' saw the courage of this young fighter, he ordered his troops to attack him in force. They surrounded him from all sides, and attacked him with swords, spears, daggers and arrows. An enemy soldier hit him on his head with such force that he fell from his horse.
Imam Hussain (pbuh) stood near the tents as he held his horse's reins. Evidently he was alert and ready. At once he heard a cry. It was Qasim: "Ya Ammah!" (O Uncle!). Imam Hussain (pbuh) flew on the horse like a hunting falcon. As he arrived by the side of Qasim, about two hundred men had surrounded this child. They fled as the Imam attacked, and one of the enemy's men who had dismounted to sever Qasim's head was himself trampled under the hoofs of the horses of his fleeing comrades. When the Imam arrived at Qasim's side, there was so much dust and confusion that nobody could see what was happening; when the dust settled down, they saw the Imam sitting at Qasim's side with his head in his arms. They heard the Imam utter this sentence: "My nephew! By God, it is very hard on your uncle that you should call him and he should not be able to respond, or that he should respond without being able to do anything for you!" It was at this moment that a cry came from this youth and his spirit departed towards its Creator.
Imam Hussein(as)
Note: The one who is said to have been trampled to death under the hoofs of the horses was one of the enemy's men, not Qasim. And the report about the wedding of Qasim to 'Fatema Kubra' the daughter of Imam Hussain (pbuh), on the night before 'Ashura' is not true. Another two sons (Abdullah and Hassan-e-Mussanna) of Imam Hassan (pbuh) were also participated in the battle of Karbala, apart from Qasim. Qasim and Abdullah were martyred, while Hassan-e-Mussanna born from Ju'ada daughter of Ash'ath survived
source : tebyan
