Is it permissible to warn people about a drunkard?

Question:
A man’s daughter was divorced by her husband, and her husband was a drunkard. He says: Is it permissible for me to warn people about him without them asking me, or must they ask me first?

Answer:
If he is asked for advice, he should give it, and giving advice is part of the advice itself. However, if he is openly committing sins, there is no backbiting in speaking about him. So if he drinks in the markets or coffee shops and does not care, there is no backbiting in speaking about him.
Q: Is he concealing it?
A: He should only advise him if he is asked for advice.
Q: So it is not permissible for him to say anything about him?
A: No, that is backbiting.