عَنْ عَبْدِ اللَّهِ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: ((لَا يَحِلُّ دَمُ امْرِئٍ مُسْلِمٍ يَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَأَنِّي رَسُولُ اللَّهِ إِلَّا بِإِحْدَى ثَلَاثٍ: الثَّيِّبُ الزَّانِي، وَالنَّفْسُ بِالنَّفْسِ، وَالتَّارِكُ لِدِينِهِ الْمُفَارِقُ لِلْجَمَاعَةِ))
Narrated by Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: The blood of a Muslim who testifies that Allah alone is the true deity and that I am the Messenger of Allah is not lawful, except in three cases: (1) a married adulterer, (2) one who is killed in retaliation for murder, and (3) one who leaves the religion and separates from the community.