lbn Mas'ud (RAA) narrated that The Messenger of Allah (ﷺ) said:
"The blood of a Muslim who testifies that none has the right to be worshipped but Allah and that I am His Messenger, cannot be shed lawfully, except in three cases: a married person who committed adultery, in Qisas (retaliation) for murder (life for life) and the apostate from Islam who abandons the Muslim Jama'ah (community)." Agreed upon. (RU)
English reference (RU): Book 9, Hadith 1199 (RU)
Arabic reference (RU): Book 9, Hadith 1169 (RU)