Shaykh Uthaymeen has said (about a Muslim ruler who has total replaced all the shariah laws of his country with man made laws and therefore only rules by man made laws that)
“…when the Hukm of Allaah is removed and replaced with another Taghoot Hukm (disbelieving law), so that the Hukm (law) of the Shariah is eliminated between the people and he puts in its place another Hukm (law) from the fabrication of the humans and they remove the laws of the Shariah concerning the Mu’amilah (i.e. the general actions between people) and they put in its place fabricated laws and this, without doubt, (this) is (total) istibdaal (replacement) of the Shariah of Allaah subhaanahuu wa-ta’ala, with other than it.
And this is (major) Kufr which removes one from the Milla (religion) because this person put himself at the level of the Creator because he shara’a (legislated) for the slaves of Allaah that which Allaah ta’ala did not give permission for and that is Shirk in His, ta’ala’s saying: “Or have they partners with Allah (false gods), who have instituted for them a religion, which Allah has not allowed?” (Ash-Shu’ara, 21) – Ref: Fiqh Al-’ Eebaadaat”, Number 60
Else were Shaykh Uthaymeen has stated: Allah has described those who do not rule by what Allaah has revealed with three descriptions: “Whosoever does not rule by what Allah has revealed then they are the disbelievers [kaafiroon].”
“Whosoever does not rule by what Allah has revealed then they are the oppressors [dhaalimoon]”
“Whosoever does not rule by what Allah has revealed then they are the sinners [faasiqoon].”
The People of Knowledge have differed concerning this.
So it is opined that these descriptions in fact describe one and the same thing because the kaafir is a dhaalim due to the saying of Allah, “And the disbelievers are the oppressors.” [al-Baqarah (2): 254]
[Similarly the kaafir] is a faasiq due to the saying of Allah, “As for the sinners then their abode will be the Fire.” [as-Sajdah (32): 20]
It is also opined that these are distinct descriptions and that they are [applied] in accordance to the situation:
So [one] becomes a kaafir in three circumstances, when he believes that it is permissible to rule by other than what Allah has revealed. The evidence for this lies in the saying of Allah, “So is it the rule of Jaahiliyyah (ignorance) that they seek?” [al-Maidah (5): 50].
Everything that opposes the rule of Allah constitutes the rule of Jaahiliyyah. [Also the evidence for this] is the definitive consensus that it is not allowed to rule by other then what Allah has revealed.
(The three situations below show when the person who rules by other than Allahs law becomes a kaafir due to comiting major kufr.)
1. Therefore the one who considers it lawful and permissible to rule by other then what Allah has revealed has contradicted this definitive consensus and such a person is a kaafir and an apostate. This (is similar to the case of one) who, considers fornication or alcohol to be permissible or considers bread or milk to be unlawful.
2. When he believes that ruling by other then what Allah revealed is equivalent (equal) to ruling by the rule of Allah.
3. When he believes that ruling by other then what Allah revealed is better than ruling by what Allah has revealed. The evidence for this lies in the saying of Allah, “And who is better than Allah in judgment for a people who have certainty?” [al-Maidah (5): 50]
So this verse states that the ruling of Allah is the best of rulings as is further proven by the saying of Allah, endorsing this, “Is Allah not the best of judges?” [at-Teen (95): 8].
So when Allah is the best of the judges in ruling and He is the most just of the rulers then whosoever claims that the rule of other than Allah is equivalent or better than the rule of Allah is a kaafir because he has denied the Quran.
(Below are the situations in which the one who rules by other than Allahs law has comited a major sin but not major kufr.)
(One) becomes a dhaalim. When he believes that ruling by what Allah has revealed is the best of judgments and the most beneficial for the servants and the lands and that it is obligatory to apply it.
However hatred and jealousy lead him to rule by other than what Allah revealed over his subjects – such a person is a dhaalim.
(One) becomes a faasiq (sinner). When he follows his own desires, for example he rules in favour of a person due to being bribed by him, or due to his being a close relative or friend, or [because the ruler] seeks the fulfillment of a need from his comrades or the likes. This along with the belief that the rule of Allaah is the ideal and it is obligatory to follow it – such a person is a faasiq. Even though he is also a dhaalim, describing him as a faasiq is more befitting.” Ref: Al-Qawl al-Mufeed `ala Kitaab at-Tawheed, 2/263-269
Posted by Abdul Kareem Ibn Ibn Ozzie