Need some advice on my 4 year old

Lately (in the past 3-4 weeks) my 4 year old boy will get mad at me if I tell him no about something, and then hurt his younger sister who is about to turn 1. It’s like he is violent with her because he knows that he is stronger and she can’t fight back. A couple examples of his aggression would be walking over to her and stomping on her hand because I told him to give me a (softish) toy that he was using to whack her, walking over to her and pushing her down because I told him to stop jumping on me, and pushing her down from sanding next to the couch that he was sitting on because I told him to stop yelling while I was trying to listen to a phone call. I have tried time out, I have tried talking to him and explaining the importance of protecting instead of hurting his baby sister, I have tried having him do something nice for her and tell her sorry. Nothing seems to be working. It’s gotten to the point where it seems that every time he has an inconvenience, he goes and hurts her. I am at the point of not letting him around her at all. I don’t know what to do. Should I take him to therapy? Just keep at trying to have him do nice things for her?