Sayyidah Aisha (may Allah be pleased with her) said: Any Muslim belonging to this Ummah can be killed for one of three reasons: a person who kills someone, so he will be killed in retaliation; a married adulterer; one who separates from the community (the narrator is in doubt, perhaps these are the words) one who leaves the community. This hadith is mawquf.
Hadith Referenceسنن الدارقطني / كتاب الحدود والديات وغيره / 3095
Hadith Takhrij«أخرجه مسلم فى ((صحيحه)) برقم: 1676، وابن حبان فى ((صحيحه)) برقم: 4407، والحاكم فى ((مستدركه)) برقم: 8131، وأبو داود فى ((سننه)) برقم: 4353،والنسائي فى ((المجتبیٰ)) برقم: 4022 ، 4053 ، 4747 ، والدارقطني فى ((سننه)) برقم: 3087، 3088، 3091، 3093، 3094، 3095، 3096، وأحمد فى ((مسنده)) برقم: 24942»