Al-Siddiq and the rest of the Companions began with jihad against the apostates before jihad against the Disbelievers from among the People of the Book. Indeed jihad against these people safeguards Muslim lands that have been granted victory, and that those who desire to depart will remain there. Jihad against the Idolaters and People of the Book who do not fight us is further manifestation of the religion. Safeguarding the capital takes precedence over profits.
Ibn Taymiyya, Majmu’ Al-fatawa [Collection of Fatwa], The book of legal punishments [hudud], Section: the rulings for apostates