From `Abdul-`Azeez ibn `Abdullaah ibn Baaz to our honorable brother, Shaykh Ahmad ibn Naasir ibn Ghunaym, may Allaah increase his knowledge and Eeman (faith) and make him blessed wherever he is. Aaameeen!
Al-salaamu ‘alaykum wa rahmatullaah wa barakaatuh (May Allaah’s Peace, Mercy, and Blessings be upon you!)
I received your letter dated 3/5/1397 A.H. (May Allaah guide you), but I was not able to read it until five or six days ago. I understood your question regarding the ruling on those who study or teach positive (man-made) law, as to whether they have committed Kufr (disbelief) or Fisq (flagrant violation of Islaamic Laws) by doing so and whether it is valid to perform Salaah (Prayer) behind them.
The answer is that there is no doubt that Allaah (Glorified be He) obligated His Servants to rule and judge according to His Sharee‘ah (Islaamic law). He warned them against resorting to other than it, and declared this as characteristic of the hypocrites. He also said that ruling by other than His Laws is the ruling of Jahiliyyah (time of ignorance) and He (Glorified and Exalted be He) clarified that there are no laws better than His. Almighty Allaah swore that the Servants will not be Mu’minin (believers) until they make His Messenger (peace be upon him) the judge in all disputes between them and find in themselves no resistance against his decisions and accept them with full submission. He (Glorified be He) also mentions in Soorah Al-Maa’idah that judging by other than what He has revealed is Kufr, injustice, and Fisq. Allaah clarifies all the proofs of what we have mentioned in His Book. As for those who study and teach such laws, they are divided into different categories… read more here.