PORTION OF BLAME H 173 "The first son of Adam bears a portion of the guilt of everyone who wrongfully kills another because he was the first to commit murder." R 173 Bukhari and Muslim with a chain up to ibn Mas'ud who related that the Prophet, praise and peace be upon him, said this.
172- وعن ابنِ مسعود رضي الله عنه : أن النَّبيّ صلى الله عليه وآله وسلم ، قَالَ : "لَيْسَ مِنْ نَفْس تُقْتَلُ ظُلْماً إلاَّ كَانَ عَلَى ابْنِ آدَمَ الأوْلِ كِفْلٌ مِنْ دَمِهَا ، لأَنَّهُ كَانَ أوَّلَ مَنْ سَنَّ القَتلَ" مُتَّفَقٌ عَلَيهِ .