an-Nisa' 4:29,93; al-Ma'idah 5:23; al-An`am 6:152; bani Isra'il 17:33
``[Jesus said:] But I tell you that anyone who is angry with his brother will be subject to judgement. Again, anyone who says to his brother 'Raca' is answerable to the Sanhedrin. But anyone who says, 'You fool!' will be in danger of the fire of hell.'' (Matthew 5:22)
Narrated Al-Ahnaf bin Qais:This hadith does not allow for the possiblity of a Muslim using the sword as defence. What about war?
While I was going to help this man ('Ali Ibn Abi Talib), Abu Bakr met me and asked, "Where are you going?" I replied, "I am going to help that person." He said, "Go back for I have heard Allah's Apostle saying, 'When two Muslims fight (meet) each other with their swords, both the murderer as well as the murdered will go to the Hell-fire.' I said, 'O Allah's Apostle! It is all right for the murderer but what about the murdered one?' Allah's Apostle replied, "He surely had the intention to kill his companion." (Sahih Bukhari 1.30)
killer who becomes a martyr also rewarded, Sahih Bukhari 4.80i