Is it permissible for rulers and judges to execute a soul in Islam?

It is not permissible for rulers, judges, or anyone else to take a life except by the right which Allah has legislated. This includes the married adulterer, a life for a life, and one who abandons their religion and separates from the community. Taking a life without right is one of the gravest sins. Allah has forbidden the taking of life except by right, and He has threatened whoever intentionally kills a believer with Hellfire. The Muslim ruler (wali al-amr) is permitted to implement Allah's prescribed punishments (hudud), such as retaliation (qisas), and discretionary capital punishment (ta'zeer bi al-qatl) in specific cases defined by Islamic law, and not according to the ruler's whims.