Is the ruling regarding one who does not govern by what Allah has revealed, or who pledges allegiance to such a ruler, considered a departure from the faith and major disbelief? And is it obligatory to advise one's father—and everyone who pledges allegiance to this party—to disassociate from it?

Ruling by other than what Allah has revealed constitutes major disbelief that expels one from the fold of Islam if a person believes that the guidance of someone other than the Prophet is more perfect than his guidance, or that the rule of someone else is better than his rule, or that man-made laws are superior to Sharia (definition) or equal to it, or that it is permissible to resort to them for judgment, or that Sharia is not suitable for application in the modern era, or that it is limited to a person's relationship with his Lord, or if he deems lawful what Allah has forbidden, which is known by necessity to be part of the religion, such as abandoning judgment by His Sharia. As for declaring a specific person to be a disbeliever, this is only valid if the conditions for declaring someone a disbeliever are met and the impediments to it are absent, such as being an adult, sane, acting out of free will, and not excused by ignorance or misinterpretation. The fundamental principle is that whoever's Islam has been established with certainty, his Islam is not removed by doubt, and a Muslim does not become a disbeliever unless he commits a statement, act, or belief that the Qur'an and Sunnah (definition) indicate to be major disbelief that expels one from the fold of Islam, or upon which the scholars have reached a consensus that it is major disbelief.