Muslim fought valiantly in the battle of Karbala, while reciting the following Rajaz: “If you inquire about me, (know that) I am a male Lion, (I am) from the chiefs and notables of the branch of Bani Asad, thus the one who oppresses us has deviated from the Right Path and from the Religion of the Self Sufficient, Omnipotent (Lord).”
He fought abundantly with the enemies and forbore upon the fight of the army until he fell down.
The narrator says that when the clouds of sand sank, Muslim was seen smeared in blood. Imam Husayn (a.s.) went to his head, when he was yet alive. Imam said,
“May your Lord have mercy upon you, O Muslim bin Awsaja! Of the believers are the men who are true to what they covenanted with Allah, of them is he who fulfilled his vow and of them is he who awaits (its fulfillment), and they have changed not in the least” (Surah al-Ahzaab, 33:23).
Then Habib bin Mazahir came to him and said, “It is very unpleasant for me to see you smeared in mud and blood O Muslim! May you receive the glad tidings of Paradise.” Then Muslim replied in a soft voice, “May your Allah give you glad tidings of fairness too.” Habib said, “If I had not known that I too would have to follow your path (of Martyrdom) and reach you, it would have been my pleasure to ask you to will to me regarding your heart’s desire, until I fulfill the rights of your relatives and your co-religionists.”
Muslim replied, “I recommend this Master for you”, he said pointing towards Imam Husayn (a.s.), “then you should ransom your life over him.” Habib replied, “By the Lord of Ka’bah! I shall surely do that.” It was not late when he died in their hands. (May Allah’s Mercy and Blessings be upon him). And one of his slave girls was heard calling out, “O son of Awsaja! O master!”
Reference : Nafasul Mahmoom – Shaikh abbas Qummi (r.a.)