Harb Al-Kirmaani (rahimahullaah) stated regarding the creed transmitted from all the Salaf that: ”If the ruler commands you an affair in which there is disobedience to Allaah, then you do not obey him at all; but you are not allowed to rebel against him nor deny him his rights.” [حادي الأرواح of Imaam Ibnul Qayyim: page: 104]
”As for rebelling against them (i.e. the rulers) and fighting them, it is forbidden by way of consensus of the Muslims (i.e. scholars of Islam) even if they (i.e. rulers) are sinful and oppressive. And indeed the ahaadeeth are manifestly clear regarding what we have mentioned and Ahlus Sunnah (i.e. the Ulama of Ahlus Sunnah) have consensus that the ruler is not removed due to (him being) sinful.” [Sharh An-Nawawi 12/229]
Shaikhul Islaam Ibn Taymiyyah (rahimahullaah) said:
”The leaders of the people of Bidah are more harmful upon the Ummah than the sinful people; so because of this the Prophet (sallal-laahu-alayhi-wasallam) commanded that the khawaarij are killed (i.e. fought and killed by the Muslim ruler) and he prohibited (us) from fighting the oppressive rulers.” [Majoo Al-Fataawaa 7/284]