"And the Fourteenth Matter is Taking the Hukm to Other than the Book of Allaah and His Messenger. " And then he mentions the Fatwaa of Ibn Katheer under the Ayaah: "Is it the Hukm of Jahileeyah which they seek?", which we have narrated earlier. Then he said, "And like this is what the general people of the Bedouins and those like them fell into with regards to taking the Hukm to the customs of their forefathers and that which their ancestors established from the accused customs, which they label 'The Sharee'ah of Reefawah' they put it before the Book of Allaah and the Sunnah of His Messenger. So whoever does that; then he is a Kaafir and it is Waajib to fight him until he returns to the Hukm of Allaah and His Messenger."
– "Majmoo'at At-Tawheed ", Pg. 412