It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Who will take responsibility for putting an end to the evil of this wicked Marhab?" Sayyiduna Muhammad bin Maslamah (may Allah be pleased with him) said: O Messenger of Allah! I am here. He (peace and blessings be upon him) said: "Go to him. O Allah, help him." So Muhammad bin Maslamah stood up. Jabir (may Allah be pleased with him) said: By Allah! I have never seen a fight between two men like the one that took place there. When the two came near each other, a tree came between them, and one of them began to take cover behind the tree to protect himself from the other. Whenever one of them was hidden, the other would reach him from behind. The two kept striking at each other again and again with their swords. Then Muhammad bin Maslamah blocked his sword's blow with his shield, and his sword got stuck in the shield, and Marhab was unable to pull it out. Then Muhammad bin Maslamah struck him and killed him. This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs did not record it, although there are mutawatir (mass-transmitted) reports with many chains of narration stating that the killer of Marhab was the Commander of the Believers, Ali bin Abi Talib (may Allah be pleased with him), one of which is the following:

It is narrated from Sayyiduna Buraydah al-Aslami (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) was encamped before the people of Khaybar, he (peace and blessings be upon him) said: "Tomorrow I will give this banner to a man who loves Allah and His Messenger, and Allah and His Messenger love him." When the next day came, a group of the Companions stretched their necks in hope of it. Then he (peace and blessings be upon him) called Sayyiduna Ali (may Allah be pleased with him), whose eyes were sore; he (peace and blessings be upon him) applied his saliva to his eyes and gave him the banner. The people advanced with him and came face to face with the people of Khaybar. There Marhab came out reciting rajaz verses, saying: "Khaybar knows that I am Marhab / fully armed, a seasoned hero; when swords come flashing like flames / I sometimes thrust with the spear and sometimes strike." Then he and Ali (may Allah be pleased with him) faced each other and exchanged two blows each. Ali (may Allah be pleased with him) struck him on the head such that the sword went down to his molars, and the people of the army heard the sound of that blow, and he killed him. The last of the people had not yet arrived when victory had already been granted to the first of them. This is a great chapter, which I have presented in detail in "al-Abwab".