Ruling on one who rules by something other than that which Allaah has revealed

The rulings on those who rule by something
other than that which Allaah has revealed vary according to their beliefs
and actions. Whoever rules by something other than that which Allaah
has revealed, thinking that it is better than the sharee’ah of Allaah,
is a kaafir according to all the Muslims. The same applies to the one
who refers for judgement to man-made laws instead of the laws of Allaah
and thinks that this is permissible. Even if he says that referring
for judgement to the sharee’ah is better, he is still a kaafir because
he has permitted that which Allaah has forbidden.

 But the one who rules
by something other than that which Allaah has revealed because he is
following his own whims and desires, or because of a bribe, or because
there is enmity between him and the one against whom judgement is being
passed, or for other reasons, knowing that he is disobeying Allaah by
doing so and that he should refer to the laws of Allaah for judgement,
is considered to be a sinner, one who is guilty of a major sin. He is
considered to have committed an act of lesser kufr, lesser wrongdoing
(zulm)  and lesser rebellion (fisq), as was narrated
from Ibn ‘Abbaas (may Allaah be pleased with him), and from Taawoos
and a group of the righteous salaf. This is well known to the scholars.
And Allaah is the Source of strength.