" لاَ يَحِلُّ دَمُ امْرِئٍ مُسْلِمٍ إِلاَّ بِإِحْدَى ثَلاَثٍ رَجُلٌ زَنَى بَعْدَ إِحْصَانِهِ فَعَلَيْهِ الرَّجْمُ أَوْ قَتَلَ عَمْدًا فَعَلَيْهِ الْقَوَدُ أَوِ ارْتَدَّ بَعْدَ إِسْلاَمِهِ فَعَلَيْهِ الْقَتْلُ "
It was narrated from Ibn 'Umar that: 'Uthman said: "I heard the Messenger of Allah [SAW] say: 'It is not permissible to shed the blood of a Muslim except in three cases: A man who commits adultery after having married; or one who kills intentionally, in which case he deserves retaliation; or one who apostatizes after having become Muslim, in which case he deserves to be killed.'"