Sayyiduna Abdullah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "It is not lawful to shed the blood of any Muslim except for one of three reasons: a married adulterer, by way of retaliation (qisas), or one who apostatizes and leaves the community."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السرقة / 17317