The recompense of  intentional murder  

 Killing intentionally the soul which Allah has forbidden is a great sin, and it is the first judgment in which the servants will be judged on the day of resurrection, where as narrated by Abdullah bin Mas'ud that Allah's Messenger (PBUH) said: "The first thing that will be decided among people on the day of resurrection will pertain to bloodshed" (Sahih Muslim 1678), and as narrated by Abdullah bin Mas'ud that the Prophet (PBUH) said: "A man will come, holding another's man hand, and will say O Lord! This man killed me, Allah will say to him Why did you kill him?, he will say I killed him so that the glory would be to You, He will say it is to Me, then a man will come holding another man's hand, and will say this man killed me, Allah will say to him Why did you kill him?, he will say so that the glory would be to so-and-so, He will say it is not to so-and-so, and the burden of sin will be upon him" (Sauna Alnasai 3997). 

  Allah Almighty says in Aya (93) of Surat Alnisa' "And whoever kills a believer intentionally, his recompense is Hellfire, abiding therein, and Allah has become angry with him, and He has cursed him and He has prepared for him a great punishment", so Allah has threatened he who kills a believer intentionally that his recompense is Hellfire, abiding therein, and Allah has become angry with him, and He has cursed him, kept him away from His Mercy, and prepared for him a great punishment in Hellfire on the day of resurrection, therefore, Allah has made an expiation for killing by mistake as mentioned in Aya (92) of Surat Alnisa', but He did not make any expiation for he who kills a believer intentionally, and as narrated by Umm Aldarda' from Abu Aldarda': ''I heard the Messenger of Allah (PBUH) as saying it is hoped that Allah may forgive every sin except in the case of one who dies a polytheist, or one who kills a believer intentionally" (Sunan Abu Dawood 4270). And Allah's Messenger assures that killing a Muslim intentionally will lead the killer to Hellfire on the day of resurrection as narrated by Alahnaf bin Qais: "I heard Allah's Messenger (PBUH) saying if two Muslims meet each other with their swords, then the killer and the killed one are in the Fire, I said O Allah's Messenger! It is alright for the killer, but what about the killed one, He said he was eager to kill his opponent" (Sahih Albukhari 6875), 

 And as narrated by Sa'id bin Jubair: "The people of Kufa disagreed about the above verse, so I went to Ibn Abbas and asked him about it, he said And whoever kills a believer intentionally, his recompense is Hellfire was revealed last of all and nothing abrogates it" (Sahih Albukhari 4590). And as narrated by Amr bin Dinar from Ibn Abbas that Allah's Messenger (PBUH) said: "On the day of resurrection, the murdered will come with the murderer's forelock and his head in his hand, and his jugular vein flowing blood saying O Lord! This one killed me until he comes close to the Throne, so they mentioned repentance to Ibn Abbas, and he recited And whoever kills a believer intentionally, his recompense is Hellfire, he said this Aya was not abrogated nor replaced, so from where is his repentance" (Jami' Altirmidhi 3029).

 It is not permissible for a believer to kill his fellow believer in any way, but it is permissible to shed a Muslim's blood in three cases, if one of them happens, it is not permissible for anyone to kill him, but that is to the Imam or those in authority, where as narrated by Abdullah bin Mas'ud that the Messenger of Allah said: "It is not permissible to take the life of a Muslim who bears witness that there is no God but Allah and that I am the Messenger of Allah but in one of three cases the married adulterer, a life for a life, and the deserter of his religion, abandoning the community (of Muslims)" (Sahih Muslim 1676).