Musnad Ahmad 334:10

Abu al-Nadr narrated to us, he said: Ikrimah narrated to us, he said: Iyas ibn Salamah narrated to me, he said: My father informed me, he said: My uncle challenged Marhab the Jew to a duel on the day of Khaybar. Marhab said: "Khaybar knows that I am Marhab, Fully armed, a tested hero, When wars approach, blazing." My uncle Amir said: "Khaybar knows that I am Amir, Fully armed, an adventurous hero." They exchanged two blows. Marhab’s sword fell upon Amir’s shield, and he went to strike low at him, but the sword returned upon his own leg and severed his main artery, and his life was in that. Salamah ibn al-Akwa said: I met some of the companions of the Prophet, may Allah bless him and grant him peace, and they said: "Amir’s deeds have been rendered void; he killed himself." Salamah said: I came to the Prophet of Allah, may Allah bless him and grant him peace, weeping, and I said: "O Messenger of Allah, Amir’s deeds have been rendered void." He said: "Who said that?" I said: "Some of your companions." The Messenger of Allah, may Allah bless him and grant him peace, said: "He who said that has lied; rather, he has his reward twice." When he went out to Khaybar, he began to recite verses for the companions of the Messenger of Allah, may Allah bless him and grant him peace, and among them was the Prophet, may Allah bless him and grant him peace, driving the camels, and he was saying: "By Allah, were it not for Allah, we would not have been guided, Nor would we have given charity, nor would we have prayed. Indeed, those who have transgressed against us, If they desire discord, we refuse. And we have not been independent of Your bounty, So make firm our feet if we meet [the enemy], And send down tranquility upon us." The Messenger of Allah, may Allah bless him and grant him peace, said: "Who is this?" He said: "Amir, O Messenger of Allah." He said: "May your Lord forgive you." He said: And he never asked for forgiveness for a person specifically except that he was martyred. When Umar ibn al-Khattab heard that, he said: "O Messenger of Allah, if only you had let us enjoy Amir." So he advanced and was martyred. Salamah said: Then the Prophet of Allah, may Allah bless him and grant him peace, sent me to Ali and said: "I will certainly give the banner today to a man who loves Allah and His Messenger, or whom Allah and His Messenger love." He said: So I brought him, leading him, while he had eye inflammation. The Prophet of Allah, may Allah bless him and grant him peace, spat into his eye, then gave him the banner. Marhab came out, brandishing his sword, and said: "Khaybar knows that I am Marhab, Fully armed, a tested hero, When wars approach, blazing." Ali ibn Abi Talib, may Allah be pleased with him, said: "I am the one whom my mother named Haydarah, Like a lion of the forests, fierce in appearance, I repay them with the measure of the *sandarah* (a large measure)." He split Marhab’s head with the sword, and the victory was at his hands.