Narrated `Abdullah: The Prophet said, "No human being is killed unjustly, but a part of responsibility for the crime is laid on the first son of Adam who invented the tradition of killing (murdering) on the earth. (It is said that he was Qabil).

Narrated `Abdullah bin `Umar: The Prophet said, "After me (i.e. after my death), do not become disbelievers, by striking (cutting) the necks of one another.

Narrated Abu Zur'a bin `Amr bin Jarir: The Prophet said during Hajjat-al-Wada`, "Let the people be quiet and listen to me. After me, do not become disbelievers, by striking (cutting) the necks of one another."

Narrated `Abdullah bin `Amr: The Prophet said, "Al-Ka`ba'ir (the biggest sins) are: To join others (as partners) in worship with Allah, to be undutiful to one's parents," or said, "to take a false oath." (The sub-narrator, Shu`ba is not sure) Mu`adh said: Shu`ba said, "Al-Ka`ba'ir (the biggest sins) are: (1) Joining others as partners in worship with Allah, (2) to take a false oath (3) and to be undutiful to one's parents," or said, "to murder (someone unlawfully).

Narrated Anas bin Malik: The Prophet said, "The biggest of Al-Ka`ba'ir (the great sins) are (1) to join others as partners in worship with Allah, (2) to murder a human being, (3) to be undutiful to one's parents (4) and to make a false statement," or said, "to give a false witness."

Narrated Usama bin Zaid bin Haritha: Allah's Apostle sent us (to fight) against Al-Huraqa (one of the sub-tribes) of Juhaina. We reached those people in the morning and defeated them. A man from the Ansar and I chased one of their men and when we attacked him, he said, "None has the right to be worshipped but Allah." The Ansari refrained from killing him but I stabbed him with my spear till I killed him. When we reached (Medina), this news reached the Prophet. He said to me, "O Usama! You killed him after he had said, 'None has the right to be worshipped but Allah?"' I said, "O Allah's Apostle! He said so in order to save himself." The Prophet said, "You killed him after he had said, 'None has the right to be worshipped but Allah." The Prophet kept on repeating that statement till I wished I had not been a Muslim before that day.

Narrated 'Ubada bin As-Samat: I was among those Naqibs (selected leaders) who gave the Pledge of allegiance to Allah's Apostle. We gave the oath of allegiance, that we would not join partners in worship besides Allah, would not steal, would not commit illegal sexual intercourse, would not kill a life which Allah has forbidden, would not commit robbery, would not disobey (Allah and His Apostle), and if we fulfilled this pledge we would have Paradise, but if we committed any one of these (sins), then our case will be decided by Allah.

Narrated `Abdullah: The Prophet said, "Whoever carries arms against us, is not from us."

Narrated Al-Ahnaf bin Qais: I went to help that man (i.e., `Ali), and on the way I met Abu Bakra who asked me, "Where are you going?" I replied, "I am going to help that man." He said, "Go back, for I heard Allah's Apostle saying, 'If two Muslims meet each other with their swords then (both) the killer and the killed one are in the (Hell) Fire.' I said, 'O Allah's Apostle! It is alright for the killer, but what about the killed one?' He said, 'The killed one was eager to kill his opponent."