In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Shaikhul Islaam Ibn Taymiyyah [rahimahullah] said:
When it is the case that the [true] followers of the Prophets are people of knowledge and justice, then the speech of the people of Islaam and the Sunnah about the disbelievers and people of bidah is to be [carried out] with knowledge and justice, and not [based on] conjecture and the soul’s desire. And due to this, the Prophet [sallal-laahu-alayhi wasallam] said, “Judges are three types; one will go to Paradise and two to Hell. A man who knows the truth and judges with it will enter paradise; a man who knows the truth but judges with the opposite of it will enter the fire, and a man who judges for the people based on ignorance will enter the fire’’. [Reported by Imaam Abu Dawud and others]
And when it is the case that the one who judges between the people in [affairs] of wealth, blood [i.e. murder cases etc] and honour will enter the hell fire if he is not a just scholar, then what about the one who passes judgements without knowledge-such being the case with ahlul bidah- on religions, the fundamental principles of Imaan, affairs of knowledge related to Allaah, His Names, Attributes and Actions, and the lofty affairs of knowledge?!’’
[Al-Jawaabus Saheeh 1/107-108]