Volume 9 · Book 92 · Hadith 423
Narrated 'Abdullah: The Prophet said, "None is killed unjustly, but the first son of Adam will have a part of its burden." Sufyan said, "..a part of its blood because he was the first to establish the tradition of murdering"
— Sahih Bukhari, Volume 9, Book 92: Holding Fast to the Qur'an and Sunnah, Hadith #423