حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، وَأَبُو بَكْرِ بْنُ خَلاَّدٍ الْبَاهِلِيُّ قَالاَ حَدَّثَنَا وَكِيعٌ، عَنِ الأَعْمَشِ، عَنْ عَبْدِ اللَّهِ بْنِ مُرَّةَ، عَنْ مَسْرُوقٍ، عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ لاَ يَحِلُّ دَمُ امْرِئٍ مُسْلِمٍ يَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنِّي رَسُولُ اللَّهِ إِلاَّ أَحَدُ ثَلاَثَةِ نَفَرٍ النَّفْسُ بِالنَّفْسِ وَالثَّيِّبُ الزَّانِي وَالتَّارِكُ لِدِينِهِ الْمُفَارِقُ لِلْجَمَاعَةِ ‏"‏ ‏.‏

It was narrated from 'Abdullah, who is Ibn Mas`ud, that the Messenger of Allah (PBUH) said: “It is not lawful to shed the blood of a Muslim who bears witness that none has the right to be worshiped but Allah (SWT), and that I am the Messenger of Allah (PBUH), except in one of three cases: a soul for a soul; a married person who commits adultery, and one who leaves his religion and splits from the Jama`ah.” Translation Not Available

Book reference: Sunan Ibn Majah Book 20 Hadith 2534
Web reference: Sunan Ibn Majah Volume 3 Book 20 Hadith 2534