An addiction is not something that you just wake up and stop doing. It takes time and the person has to be willing to quit. You mentioned rehab like you don't live in Nigeria. How is smoking affecting his work? Does he smoke while working and mind you some companies allow staff to take a break and smoke outside. Do not report him to anyone against his will, he is an adult not your child or ward. Just admit that you don't like it personally which is understandable but be gentle about it with him instead of going the reporting way,if you report him it would either make him resent you or start hiding it from you. Also, you need to be sure that he even wants to quit, it's possible he told you that to placate you. If smoking is a deal breaker for you then you know what to do. Many people quit smoking and pick it up again.