Is it permissible to buy cigarettes or any other forbidden thing for one's father if he asks for it?

You are not permitted to help your father buy cigarettes for him, due to the Almighty’s saying: (And do not cooperate in sin and aggression). This is unless you believe that not fulfilling his request will lead to a greater harm, in which case it is permissible to buy cigarettes for him while continuing to advise him.

However, if he asks you for something greater than cigarettes, such as alcohol or drugs, you must refuse to fulfill his request, even if it leads to your expulsion from the house. If you are able to support yourself, then leave. If you are not able, then you may resort to a judge to protect you and preserve your rights.