You could explain that hitting hurts or even ask him how he feels when someone hits him. Then reinforce the importance of using words to get your point across. Be prepared for the child that can tell you the rules and even the consequences but still follows their impulse. Unfortunately, we are seeing more and more children that only catch or retain part of what we are saying. This may seem like a small change, and it really is, but it can make the world of difference in a child's behavior.
Positive reinforcement works.
It is retraining us, the care provider, on how we address the situation and how we respond. Think of what the child should be doing and try to respond in that mode rather than what they're doing wrong. Yes, safety and order. It is important to talk about and implement proper behavior. Rules need to be short and simple and have natural or logical consequences.