Shaykh Saalih Al-Fawzaan (hafidahullah) was asked:

Does disbelief have many types and levels, some of them more severe than others? Or is it one level? And if there are levels of disbelief, then which of them constitutes cursing of the religion, or Allah, or the Messenger (sallallaahu alaihi wa sallam), and refuge is sought with Allah from that?

He answered:

Yes, Disbelief, – refuge is sought with Allah – is levels, some of them more severe than others, from them is disbelief which exits from the religion, and from them disbelief which is lesser than that: Lesser disbelief. Cursing of the religion, or cursing Allah, or His Messenger (sallallaahu alaihi wa sallam) this is from major disbelief, that exits from the religion – refuge is sought with Allah -.

As for lesser disbelief, then its example is like his saying (sallallaahu alaihi wa sallam)

“Cursing a Muslim is sin, and killing him is disbelief.” (1)

And his statement (sallallaahu alaihi wa sallam):

“So, do not turn to disbelief after me by striking the necks of one another” (2)

This is from lesser disbelief which doesn’t exit from the religion, so killing a person is a terrible crime, a great sin and a great prohibition, however it does not lead to the level of disbelief which exits from the religion.

• Al-Bukhaari 6044, Muslim 64
• Al-Bukhaari 121, 1739, Muslim 65, 66

Majmoo’ Fataawa lish Shaykh Saalih Al-Fawzaan (hafidahullah) Vol. 1 Page 14-15