What is the ruling on one who intentionally takes a life, and what was the situation of the Companions regarding this? Is it permissible to kill an unjust ruler or to rebel against him? Is it permissible to shed the blood of a Muslim for any reason other than the three mentioned in the Prophet's hadith, for the sake of some perceived benefit?

Unlawfully taking a life is one of the gravest major sins. The general principle is that it is not permissible to kill a Muslim except in one of three cases: the married fornicator, a life for a life, and one who abandons their religion and separates from the community. Exceptions to this include certain issues explicitly mentioned by scholars where killing is permitted as a discretionary punishment (ta'zeer), such as killing a Muslim spy if they spy against Muslims. Some jurists have permitted ta'zeer by killing in specific crimes under certain conditions, such as one who repeatedly commits sodomy or kills with a heavy object, and a corrupt individual (mufsid) if their evil cannot be stopped except by killing them. As for the fighting that occurred among the Companions, it does not fall under this category; rather, it was fighting among those who held different interpretations, and all of them sought the truth. The stance of the Ahl al-Sunnah is to refrain from discussing it and to avoid delving into it.