(1) باب قَوْلِ اللَّهِ تَعَالَى {وَمَنْ يَقْتُلْ مُؤْمِنًا مُتَعَمِّدًا جَزَاؤُهُ فَجَهَنَّمُ}
Narrated Ibn `Umar:
Allah's Messenger (ﷺ) said, "A faithful believer remains at liberty regarding his religion unless he kills somebody unlawfully."
Reference: Sahih al-Bukhari 6862
In-book reference: Book 87, Hadith 2
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 83, Hadith 2