مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3606
Musnad of Abdullah bin Mas'ood
It was narrated that `Abdullah said: The Messenger of Allah (ﷺ) said: “No soul is killed unlawfully, but there is a share of the sin on the first son of Adam, because he was the first one to set the precedent of killing."
Musnad Ahmad 3630Its isnad is saheeh, al-Bukhari (3335) and Muslim (1677)]