Revelation 13:15-18

15And it was allowed to give breath to the image of the beast, so that the image of the beast might even speak and might cause those who would not worship the image of the beast to be slain. 16Also it causes all, both small and great, both rich and poor, both free and slave, to be marked on the right hand or the forehead, 17so that no one can buy or sell unless he has the mark, that is, the name of the beast or the number of its name. 18This calls for wisdom: let the one who has understanding calculate the number of the beast, for it is the number of a man, and his number is 666.