"I heard Mu'awiyah delivering the Khutbah, and he narrated a few Hadiths from the Messenger of Allah say: Every sin may be forgiven by Allah except a man who kills a believer deliberately, or a man who dies as a disbeliever.'"
Sunan an-Nasa'i Book 37, Hadith 19
← Previous Hadith 'Amr bin Aws told him that his father Aws said: "The Messenger of Allah said: 'I have been commanded to fight the people until they bear witness to La ilaha illallah (there is none worthy of worship except Allah), then their blood and their wealth become forbidden to me, except for a right that is due."

Sunan an-Nasa'i Book 37, Hadith 18 Next Hadith → The Prophet said: "No person is killed wrongfully, but a share of responsibility for his blood will be upon the first son of Adam, because he was the first one to set the precedence, of killing."

Sunan an-Nasa'i Book 37, Hadith 20