When Moses was a full 40 years old (Acts 7:23) he came upon an Egyptian who was beating an Israelite slave. He looked around and not seeing anyone else he killed the Egyptian and buried him in the sand. He later learned that what he had done was public knowledge and so he fled Egypt and went to Midian. (Exodus 2:11-15)
For further study, (if you have not read it already) read: