(V.5:44) For different degrees of Kufr (Disbelief) see Appendix 2, "Polytheism and Disbelief".
(V.5:45) Narrated ‘Abdullâh رضي الله عنه: Allâh’s Messenger صلى الله عليه وسلم said, "The blood of a Muslim who confesses that Lâ ilaha illallâh (none has the right to be worshipped but Allâh) and that I am the Messenger of Allâh, cannot be shed except in three cases.
1) Life for life in case of intentional murder without right [i.e. in Qisâs (Law of Equality in punishment)],
2) A married person who commits illegal sexual intercourse, and
3) The one who reverts from Islâm (apostates) and leaves the group of Muslims (by innovating heresy, new ideas, new things in the Islâmic Religion). (See Fath Al-Bari Vol. 15, page No.220, for details). (Sahih Al-Bukhâri, Vol.9, Hadîth No.17).