28. The Book of Oaths, Muharibin, Qasas (Retaliation), and Diyat (Blood Money) - كتاب القسامة والمحاربين والقصاص والديات
7) Chapter: The sin of the one who set the precedent of killing
'Abdullah (b. Mas'ud) reported:
Allah's Apostle (ﷺ) having said: No person who is killed unjustly, but the share of (this offence of his also) falls upon the first son of Adam, for he was the first to introduce killing.