مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4065
Musnad of Abdullah bin Mas'ood
It was narrated from 'Abdullah that The Prophet (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 4092Its isnad is saheeh, al-Bukhari (6867)]