Is it permissible to greet a person who is committing a sin?

Question:
Some people may see a person who is an open sinner, or... or who lets his garment hang below the ankles, and they do not greet him?

Answer:
No, it is prescribed to greet him and advise him, for he may be ignorant. The Sunnah is to greet him, because it brings familiarity and closeness, and it is also a key to giving advice. This is except if he is stubborn, and he knows that he is stubborn, and you see that boycotting him is better, and that it has an effect on him and benefits him. And if you see that boycotting him is not better, and that continuing to advise him and enjoining good and forbidding evil is more beneficial, then do what is better.
Q: If one passes by a smoker, does he greet him?
The Shaykh: Yes, you greet him and advise him, making it clear to him that this is what is wrong.