Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) narrates that on the day of Khaybar his brother fought fiercely alongside the Messenger of Allah (peace and blessings be upon him); then his sword rebounded on him and killed him. The Companions of the Messenger of Allah (peace and blessings be upon him) said about this: He died by his own weapon; and they had some doubts about his affair. Sayyiduna Salamah (may Allah be pleased with him) says: When the Messenger of Allah (peace and blessings be upon him) returned from Khaybar, I said to him (peace and blessings be upon him): O Messenger of Allah! Will you permit me to recite rajaz verses before you? The Messenger of Allah (peace and blessings be upon him) gave me permission. Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) said: Watch what you are saying. So I recited this rajaz: "By Allah! Had it not been for Allah, we would not have been guided, nor would we have given charity, nor prayed." The Prophet (peace and blessings be upon him) said: "You have spoken the truth." "So send down tranquillity upon us, and make our feet firm if we meet (the enemy). The polytheists have transgressed against us; they said: Disbelieve! We said: We refuse." The Prophet (peace and blessings be upon him) asked: "Who composed these verses?" I said: My brother. The Prophet (peace and blessings be upon him) said: "May Allah have mercy on him." I said: O Messenger of Allah! By Allah, some people are hesitant to offer the funeral prayer over him, and they say: This man died by his own weapon. The Messenger of Allah (peace and blessings be upon him) said: "He died striving, as a mujahid." Muhammad bin Muslim al-Zuhri says: Then I asked the son of Salamah bin al-Akwa', and he narrated to me from his father the same as what Abd al-Rahman had narrated to me, except that Ibn Salamah also said: The Messenger of Allah (peace and blessings be upon him) said: "He died striving, as a mujahid, and he will have two rewards." And the Messenger of Allah (peace and blessings be upon him) gestured with his two fingers and moved them.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6202