Revelation 13:17

17 No one could buy or sell without this mark, that is, the beast's name or the number that stands for the name.

Revelation 13:17 In-Context

15 The second beast was allowed to breathe life into the image of the first beast, so that the image could talk and put to death all those who would not worship it.
16 The beast forced all the people, small and great, rich and poor, slave and free, to have a mark placed on their right hands or on their foreheads.
17 No one could buy or sell without this mark, that is, the beast's name or the number that stands for the name.
18 This calls for wisdom. Whoever is intelligent can figure out the meaning of the number of the beast, because the number stands for the name of someone. Its number is 666.
Scripture taken from the Good News Translation - Second Edition, Copyright 1992 by American Bible Society. Used by Permission.