Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. d3/5...b5/6. Bb3

6. Bb3
This retreats the bishop to the only good square. It puts it on a good square where it controls the a2-g8 diagonal.