One who did argue this was Muhammad abd-al-Salam Faraj, the main theoretician of the Islamist group that assassinated Egyptian President Anwar Sadat. who in his book "Al-Farida al-gha'iba" (The Neglected Duty), cited a fatwa issued in 1303 CE by the celebrated strict medieval jurist Ibn Taymiyyah. He had ruled that fighting and killing of the Mongol invaders who were invading Syria was not only permitted but obligatory according to Sharia. This was because the Mongols did not follow sharia law, and so even though they had converted to Islam (Ibn Taymiyyah argued) they were not really Muslims. Faraj preached that rulers such as Anwar Sadat were "rebels against the Laws of God [the shari'ah]", and "apostates from Islam" who have preserved nothing of Islam except its name.