Is it permissible for a Muslim who believes in the Qur’an and Sunnah according to the understanding of the Companions and their Successors, and who supports Ali ibn Abi Talib, then Al-Hasan, then Mu’awiyah, then Al-Hussein, to refrain from pledging allegiance to a new ruler who has not yet consolidated power, due to his blatant disbelief or his allegiance to disbelievers, by analogy with the action of Al-Hussein ibn Ali?

The questioner's confusion regarding the issue of Husayn's departure, and his assumption that those who opposed his departure, such as Ibn Umar and Ibn Abbas - who were among the most virtuous scholars and religious figures - had no evidence, is mistaken on two counts. The opposition of the Companions was not devoid of Shariah-based evidence, and Husayn's departure, despite his good intentions, was not more guided than his brother Hasan (definition)'s relinquishing of the caliphate. The consensus of the Sunnis has settled on the prohibition of taking up arms against an unjust or tyrannical Muslim ruler.