He is stunned. He can't believe it. John tells him that Abby was the one to confess that it had "naught to do with witchcraft", but it is Abby who is the one who is leading most of the charges. Hale is incredulous, and has a hard time believing it. His first reaction is one of clarification-he makes Proctor clarify that it was indeed Abigail Williams who had said that. Then, immediately, he becomes suspicious of John. He asks, suspiciously, "Why-why did you keep this?" He wonders why John would not have told anyone about this before. His suspicious turns to disbelief. He doesn't believe it. He states, "Nonsense!" and goes on to explain that he himself has examined several women how "have confessed" witchcraft. John points out that why wouldn't they, "if they must hang for denyin' it?" Hale concedes this point, anda acknowledges that that very thought had crossed his mind, then asks John, "would you testify to this in court?" His starting to believe Proctor; he wants to believe him. He then turns to questioning his character even more thoroughly, to try to get a better grasp on him.
So, Hales reaction starts with incredulity, turns to suspicion, to disbelief, to a desire to believe. I hope that helps! Good luck!