Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) narrates: Sayyiduna Amir bin al-Akwa' (may Allah be pleased with him) dueled with a man, struck him and killed him, but the sword struck Amir's own leg. He said: I have killed myself. Then he died. When this was mentioned to the Prophet (peace and blessings be upon him), he (peace and blessings be upon him) said: "He will have a double reward."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6247