Revelation 13:16-18

Darby Translation

¹⁶ And it causes all, the small and the great, and the rich and the poor, and the free and the bondmen, that they should give them a mark upon their right hand or upon their forehead;

¹⁷ and that no one should be able to buy or sell save he that had the mark, the name of the beast, or the number of its name.

¹⁸ Here is wisdom. He that has understanding let him count the number of the beast: for it is a man's number; and its number [is] six hundred [and] sixty-six.