John Gill Commentary Acts 26:12

"Whereupon as I journeyed to Damascus with the authority and commission of the chief priests," — Acts 26:12 (ASV)

Whereupon as I went to Damascus
Being intent, upon the above said things, to punish the saints, compel them to blaspheme, imprison them, and even put them to death on account of these things; upon this errand and business he went to Damascus, the chief city of Syria, where he knew there were many that believed in Christ, who had removed from Jerusalem thither, on account of the persecution, or were settled there before:

with authority and commission from the chief priests ;
the Jewish sanhedrim, to bring those of them at Damascus bound to Jerusalem, in order to be punished, as in (Acts 9:2) (22:5) and which the Ethiopic version adds here.