Revelation 13:17
and that no one would be able to buy or to sell unless he has that mark, which is the name of the beast or the number of his name.
World English Bible (Public Domain)
In context
Before · Revelation 13:15–16
15It was given to him to give breath to the image of the beast, that the image of the beast should both speak, and cause as many as wouldn’t worship the image of the beast to be killed. 16He causes all, the small and the great, the rich and the poor, and the free and the slave, to be given marks on their right hands or on their foreheads;
17and that no one would be able to buy or to sell unless he has that mark, which is the name of the beast or the number of his name.
After · Revelation 13:18
18Here is wisdom. He who has understanding, let him calculate the number of the beast, for it is the number of a man. His number is six hundred sixty-six.