The Ruling on Greeting Sinners and Sitting with Them

Question:
Some people, when they pass by a man who has shaved his beard or is smoking, do not greet him?

Answer:
What is prescribed is that he should greet him, instruct him, advise him, direct him to good, and teach him what he does not know.
Q: Meaning, nothing prevents him from greeting...?
The Shaykh: He should greet, and advise those you know and those you do not know, saying: "My brother, do you see that this is not permissible? It is obligatory for you to let your beard grow, it is obligatory for you to stop smoking, to stop drinking intoxicants."
Q: A lot, O Shaykh... is it feasible for him to stop with every single one?
The Shaykh: To the extent of his ability, to the extent of his ability.
Q: But the greeting?
The Shaykh: It appears that he should greet, whether he knows them or not; it is general, because they may be ignorant and the proof has not been established against them.
Q: But does he sin if he sits with them without advising them?
The Shaykh: That is what appears to be the case, if he is sitting with the people of evil and does not forbid them, he is a partner with them. We ask Allah for safety.