Throughout Acts, the concepts of faith and repentance were so inseparable that the apostles had no hesitation describing the same event with both words. I’ve also heard it said that how could there be a turning to God (faith) if there is not a turning from sin (repentance)?
Additionally, think about this: What did the apostles and Luke see as they went about preaching the gospel that led them to conclude that some people had believed—In pretty much every case, there is a repentant action. In Acts 17, the believers joined the apostles amidst the others who were sneering at them or others who remained unconvinced. In Acts 2, the believers were baptized in the name of the Lord Jesus Christ—a name they despised just weeks before that. Thus, faith and repentance are like the two wheels of a bicycle—as one goes, so does the other. And if you don’t have one of those wheels, you don’t have a bicycle, but a unicycle, which is very wobbly and leads to falling.