"It is not permissible to kill a Muslim except in one of three cases: A adulterer who has been married, who is to be stoned; a man who kills a Muslim deliberately; and a man who leaves Islam and wages war against Allah, the Mighty and Sublime, and His Messenger, who is to be killed, crucified or banished from the land." (Using translation from Nasāʾī 4743)
عَنْ رَسُولِ اللهِ ﷺ أَنَّهُ قَالَ لَا يَحِلُّ قَتْلُ مُسْلِمٍ إِلَّا فِي إِحْدَى ثَلَاثِ خِصَالٍ زَانٍ مُحْصَنٍ فَيُرْجَمُ وَرَجُلٌ يَقْتُلُ مُسْلِمًا مُتَعَمِّدًا فَيُقْتَلُ وَرَجُلٌ يَخْرُجُ مِنَ الْإِسْلَامِ فَيُحَارِبُ اللهَ وَرَسُولَهُ فَيُقْتَلُ أَوْ يُصْلَبُ أَوْ يُنْفَى مِنَ الْأَرْضِ