Do I need to file a 1042/1042-S when paying a foreign contractor who performed the entire work outside of the US (and completed a W8-BEN)?

For a foreign contractor working outside the U.S., you do not need to file form 1042/1042-S. You do not need to file form 1099-NEC either. And he is not required to complete form W8-BEN.

There is no tax withholding requirement for a foreign contractor working outside the U.S.