Shaikh ul-Islaam Ibn Taymiyyah said: And it is known by necessity in the Deen of the Muslims and by the agreement of all the Muslims that whoever follows a Sharee'ah other than the Sharee'ah of Muhammad then he is a Kaafir and it is like the Kufr of the one who believes in some of the Book and disbelieves in some of the Book." "Al-Fataawa", Vol. 28/ 524 Al-Haafidh Ibn Katheer said: "So whoever leaves the clear Sharee'ah, which was revealed to Muhammad Ibn Abdullah, the Seal of the Prophets, and takes the Hukm to other than it from the laws of Kufr which are abrogated, he has disbelieved. So what about the one who takes the Hu...