The meaning of the unity of judicature
Question

                What is your view of the denial of the unity of judicature (Tawheed al-Haakimiyyah)? Is counting it as a separate category (of Tawheed) contrary to the teachings of the Salaf? Under what types of Tawheed is this matter counted?
Praise be to Allah.It 
          is not permissible to deny the unity of judicature, because it is one 
          of the types of Tawheed, but it comes under the heading of unity of 
          worship (Tawheed al-‘Ibaadah) with regard to the ruler when he rules 
          according to sharee’ah. But with regard to this concept (Tawheed), it 
          comes under the heading of the unity of Lordship (Tawheed al-Ruboobiyyah), 
          because the Ruler is Allaah, may He be exalted. 
The 
          Lord Who is in control of all things has to be the Ruler, so it comes 
          under the heading of Tawheed al-Ruboobiyyah as far as rulings, commands, 
          prohibitions and control are concerned. But with regard to implementation 
          and acting upon it, a person is obliged to follow the rulings of Allaah, 
          thus it comes under the heading of Tawheed al-‘Ibaadah in this regard. 
There 
          is no reason to make it a fourth category of Tawheed, because it is 
          included in the three existing categories. There is no need to add further 
          categories. The matter is easy to understand anyway, but if a person 
          wishes to study the issue of judicature (al-haakimiyyah) separately, 
          he will find that it is synonymous with other concepts, but that is 
          fine.