According to Kenneth R. Timmerman's book, "Preachers of Hate: Islam and the War on America," and his Washington Times article "Truth from the mouths of terrorists" [4] (published June 19, 2003), the sixth pillar of Islam is violent jihad. In Timmerman's words, "Think of it: Murder has become the sixth pillar of Islam, according to the terrorists. Where are the Muslim leaders to denounce this?"
The phrase has also been used by orientalists, and some Muslims, although the meanings plainly can differ widely.