Revelation 13:16-17

16And he causes all, 1the small and the great, and the rich and the poor, and the free men and the slaves, 2to be given a 3mark on their right hand or on their forehead,

17and he provides that no one will be able to buy or to sell, except the one who has the 4mark, either 5the name of the beast or 6the number of his name.