All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
When smoking first appeared, the jurists differed in opinion on its ruling. The reason of this difference of opinion is that some jurists are of the view that smoking is not harmful to the body and they allowed it, whereas some others are of the view that it harms the body, so they prohibited it.
However, now it is medically proven without any doubt that smoking is harmful to the body. Therefore no one should differ about its prohibition, especially that it is considered as a slow killing for the person due to the fatal diseases which it causes. The general rule among the scholars is that every thing which is believed that it most likely causes harm is forbidden in Islam.
Allaah Knows best.