Is smoking haram in Islam or makrooh (disliked)? As far as smoking is concerned, several years before… when science hadn’t advanced that far, most of the scholars used to say that smoking is makrooh (disliked) based on the Hadith of Muhammad (ﷺ) which is mentioned in Sahih Bukhari, Volume no 1, in the Book of Adhan, Hadith no. 855, where the Prophet (ﷺ) said that,
Anyone who eats garlic or onion, they should stay away from us and stay away from the mosque. 
Prophet (ﷺ) said that you know, “Don’t come to the mosque after having garlic or onion because there’s bad breath”. When you are smoking, the breath is worse than onion or garlic. So based on this Hadith, therefore, garlic and onion don’t become haram (forbidden), it becomes makrooh (disliked). So based on this Hadith, scholars give the fatwa (Islamic Ruling) that smoking is makrooh (disliked).
But now, after science has advanced, we have come to know that smoking is nothing but it’s a slow poisoning. Tobacco in any form, whether in smoking cigarettes, whether “Biri”, whether tobacco in “Hokkah” whether chewing tobacco, all forms of tobacco contain nicotine and tar, and we know its nothing but slow poisoning. That’s the reason most of the non-muslims also, they agree that smoking is haram (forbidden). Not only the Muslim world, even the non-Muslims. That’s the reason they put a statutory warning on the cigarette packs, they put a statutory warning saying, “Cigarette smoking is injurious to health”. Or in some countries, it mentions, “General surgeon’s warning” or “Surgeon general’s warning: Smoking is injurious to health.” And anyone gives an ad, whether in a newspaper or in the magazine or television, it is compulsory that they have to highlight this statement, “Smoking is injurious to health.”
So I am not talking about the Muslim world, even the non-Muslim world agrees that smoking is nothing but slow poisoning. And today according to the statistics, the WTO says that every year more than 4 million people die only because of smoking and if you count the other form of tobacco it will be much more. And, today medical science tells us and even I had learned when I was doing my medicine in the medical college that more than 90% of the lung cancer deaths are only due to smoking. Whether cigarette or biri, whatever it is 25% of the cardiovascular deaths are only because of smoking.
70%-75% of bronchitis and related deaths are only because of smoking. Smoking is nothing but slow poisoning. It blackens your lips, blackens your gums, your fingertips. It damages your lips, it damages your esophagus, it damages your stomach and it can cause constipation. It can cause loss of appetite, it can cause loss of libido the sexual power gets suppressed, it can cause immunity to the drugs (medicines) you take and reduces the defense of your body. There are today more than 400 fatwa’s, that majority of the scholars, they agree that smoking is haram (forbidden), and all form of tobacco is haram (forbidden). Allaah says’s in the Quran in Surah Al Araaf, Chapter no 7, Verse no 157,
Those who follow the Messenger, the unlettered prophet, whom they find written in what they have of the Torah and the Gospel, who enjoins upon them what is right and forbids them what is wrong and makes lawful for them the good things and prohibits for them the evil and relieves them of their burden and the shackles which were upon them. So they who have believed in him, honored him, supported him and followed the light which was sent down with him – it is those who will be the successful. 
That you follow the Prophet (ﷺ), the unlettered Prophet (ﷺ) who is most mentioned in your law and scriptures, and further it says that this Prophet (ﷺ) ask you to do things which are good for you, tayyeb for you. So take what he gives it to you, So what our Prophet (ﷺ) gives, what he gives you which is good, take and he prohibits you things which are khabees, unlawful. You have to abstain from it. This is a law and Allaah say’s in the Quran, Surah Al Baqarah, Chapter no 2, Verse no 195,
And spend in the way of Allaah and do not throw (yourselves) with your (own) hands into destruction (by refraining) and do good; indeed, Allaah loves the doers of good. 
Make not your own hands the cause of your own destruction. Indicating that do not kill your own self, because smoking is nothing but slow poisoning. It comes under this category, smoking like suicide, slow poisoning. Every puff you take you reduce your life. So based on this there are more than 400 fatwa’s saying that smoking is haram. And furthermore, this is one of the major reasons why it is haram. Furthermore, Allaah say’s in the Quran in Surah Al Araaf, Chapter no 7, Verse no 31,
O children of Adam, take your adornment at every masjid, and eat and drink, but be not excessive. Indeed, He likes not those who commit excess. 
Eat and drink, but do not be extravagant. Allaah say’s in Surah Al Israa, Chapter no 17, Verses no 26-27,
And give the relative his right, and (also) the poor and the traveler, and do not spend wastefully. Indeed, the wasteful are brothers of the devils, and ever has Satan been to his Lord ungrateful. 
That do not be extravagant, do not be spendthrift, for verily a person who’s a spendthrift is a brother of the Satan, is a brother of the devil. And we know that when we smoke its nothing but extravagance. It is nothing but taking a pound note or a few pounds or taking a dollar note. The green dollar bill or a pound and lighting up with fire. When we smoke, when we light this cigarette, its nothing but burning money. Whether it be rupees, whether its dollars, whether it pounds, whether it be riyals, it’s nothing but extravagance which is haram (forbidden) in Islam. And you can give a list of reasons why it is haram (forbidden). But just to cut it short, one more reason that you cannot harm your own neighbor. You cannot harm your own brother. And in smoking, when you exhale out the smoke, it causes more damage to your neighbor. Passive smoking is more dangerous than active smoking. When the person who smokes, when he exhales out if the person who’s a neighbor inhales this smoke, it causes more damage to him than the person who smokes. That’s the reason many courtiers like Singapore etc. They have banned smoking in public places. So based on this it is haram (forbidden), so smoking is haram (forbidden).
[The whole article takes from the lecture of this video…]