"It is not permissible to shed the blood of a Muslim except in one of three cases: A soul for a soul, a adulterer who has been married, and one who separates leaving his religion." (Using translation from Nasāʾī 4721)
عَنِ النَّبِيِّ ﷺ قَالَ لَا يَحِلُّ دَمُ مُسْلِمٍ إِلَّا بِإِحْدَى ثَلَاثٍ النَّفْسُ بِالنَّفْسِ وَالثَّيِّبُ الزَّانِي وَالتَّارِكُ دِينَهُ الْمُفَارِقُ