I have seen majority of Shia people at Imam Bargah smoking standing just outside. Isn't smoking prohibited in Islam?
This is a bit complex. And the way I have understood this is that it depends on the individual's understanding and belief regarding the damages smoking could cause to them.
To elaborate, if a beginner knows and believes that smoking could cause serious harm to him in the future then it is haram for him to smoke.
For the habitual smokers if it could be equally, or more, harmful to quit smoking than to continue then they should try to find a balance between quiting and continuing at the same pace. Else they should quit.
Question: Medical literature states that smoking is the main cause for heart and cancer diseases, and it also shortens the life span of the smoker. So, what is the rule on smoking concerning (a) the beginner, (b) the compulsive smoker, and (c) the passive smoker? In the third case, the medical experts say that the smoke also harms a person sitting besides a smoker. What would be, the ruling if he considers passive smoking to be of considerable harm?
Answer: Smoking becomes harãm for the beginner if it entails serious harm, even at the future, regardless of whether that serious harm is certain, most probable, or just probable so much so that sensible people would demand caution. However, with the protection from serious harm (for example, by smoking less frequently), there is no problem in it. If continuing to smoke will cause serious harm to the compulsive smoker —as explained above— it is necessary for him to refrain from it unless the harm in quitting is similar, greater than to the harm in continuing, or the great difficulty that he will face in quitting is such that it cannot be normally tolerated. The same rule as explained in (a) for the beginner, applies in this case also.
* There is overwhelming evidence on the dangers to health posed by smoking. Is it permissible for a non-smoker to take up the habit and a smoker to continue?
- If smoking results in an untold damage to the health of the smoker, and that of the unborn child of a smoking woman, it is haraam. And it is so, for the beginner, as well as the compulsive smoker who might not suffer serious damage as a result of stopping smoking. As for him who may be harmed, in any way, as a result of stopping the habit, the right balance between kicking the habit and continuing it should be achieved.
Source: Grand Ayatullah Sayyid Ali Husaini Sistani
As @Bleeding Fingers correctly mentioned, this is a bit complex and actually this depends upon the individual's belief and perception concerning its damages.
For instance, Ayatollah Khamenei (as a famous Shia scholar/cleric) answered a question regarding that, and said:
“The rule with various levels of harms that followed by using tobacco, are different. And in general, if the using of tobacco was that much which caused a remarkable harm for the body it isn't allowed. And if person knows that by starting smoking it will reach that level, isn't allowed.”
Ayatollah Makarem-Shirazi said regarding that:
“The rule of eating or drinking something that has serious harm, is forbidden. If using cigarettes and other forms of tobacco are considered seriously harmful by those who have the knowledge than it is forbidden. Using drugs is completely forbidden; ether by injection or smoking or eating or any other way. Also the making of, traffic, and every form of assistance in its distribution is forbidden.”
Other maraje taqlid have the same view about it – that if it has serious harm it is forbidden.
Consequently, it seems that its prohibition can be related to the individuals/conditions, for instance it can be more harmful for the persons who just started using it in comparison with the ones who are actually a kind of addict to them...