Ruling on praying behind someone who smokes
Question

                Is it valid to pray behind an imam who smokes, knowing that there are other mosques, but all the imams smoke?.
Praise be to Allah.Smoking is haraam, and 
    there is no doubt about that among the scholars. It is harmful and there is 
    no doubt about that among doctors and those who are wise. If the imam of a 
    mosque does this deed, this is regarded as committing sin openly, and some 
    scholars say that people should not pray behind him; the correct view is 
    that it is permissible, but someone else who is of good character is 
    better. 
Shaykh ‘Abd al-‘Azeez ibn 
    Baaz (may Allaah have mercy on him) was asked: 
What is the ruling on 
    smoking, and the ruling on people who do that openly leading prayers? 
He replied: 
The shar’i evidence 
    indicates that smoking is something which is forbidden, because it involves 
    many evils and harmful effects, and Allaah has only permitted to His slaves 
    food and drink which are good and beneficial. As for that which will harm 
    their spiritual or worldly interests or alter their minds, Allaah has 
    forbidden it to them, and He is more merciful towards them than their own 
    selves, and He is All-Wise and All-Knowing in His words, deeds, laws and 
    decrees. He does not forbid anything in jest or create anything in vain, and 
    He does not enjoin anything that is not of benefit to His slaves, because He 
    is the wisest of the wise and the most Merciful of those who show mercy, and 
    He knows what is in the best interests of His slaves and will benefit them 
    in this world and in the Hereafter, as He says (interpretation of the 
    meaning): 
“Certainly your Lord is 
    All‑Wise, All‑Knowing”
[al-An’aam 6:83] 
    
“Verily, Allaah is Ever 
    All‑Knowing, All‑Wise”
[al-Insaan 76:30]
And there are many similar 
    verses. 
Among the Qur’aanic 
    evidence that smoking is haraam is the verse in Soorat al-Maa’idah in which 
    Allaah says (interpretation of the meaning): 
“They ask you (O 
    Muhammad (peace and blessings of Allaah be upon 
    him)) what is lawful for them (as food). Say: 
    Lawful unto you are At‑Tayyibaat [all kinds of Halaal (lawful‑good) foods 
    which Allaah has made lawful (meat of slaughtered eatable animals, milk 
    products, fats, vegetables and fruits)]”
[al-Maa'idah 5:4]
And He says in Soorat 
    al-A’raaf, describing our Prophet Muhammad  (peace and blessings of 
    Allaah be upon him): 
“he commands them for 
    Al-Ma‘roof (i.e. Islamic Monotheism and all that Islam has ordained); and 
    forbids them from Al-Munkar (i.e. disbelief, polytheism of all kinds, and 
    all that Islam has forbidden); he allows them as lawful At‑Tayyibaat (i.e. 
    all good and lawful as regards things, deeds, beliefs, persons and foods), 
    and prohibits them as unlawful Al‑Khabaa’ith (i.e. all evil and unlawful as 
    regards things, deeds, beliefs, persons and foods)”
[al-A’raaf 7:157]
In these two verses, Allaah 
    explains that He has only permitted to His slaves things that are good and 
    lawful (al-tayyibaat), which refers to beneficial foods and drinks. As for 
    harmful foods and drinks, such as intoxicants, drugs and all kinds of foods 
    and drinks which cause spiritual or physical or mental harm, they are among 
    the evil and unlawful things (al-khabaa’ith) that are forbidden. Doctors and 
    others who are wise are unanimously agreed that smoking is something that 
    causes a great deal of harm. They have stated that it causes many diseases 
    such as cancer, stroke, etc. Anything that is of this nature is undoubtedly 
    haraam and must be avoided. No wise man should be deceived by the fact that 
    there are many people who smoke. Allaah says in His Book (interpretation of 
    the meaning): 
“And if you obey most of 
    those on the earth, they will mislead you far away from Allaah’s path. They 
    follow nothing but conjectures, and they do nothing but lie”
[al-An’aam 6:116] 
“Or do you think that 
    most of them hear or understand? They are only like cattle _ nay, they 
    are even farther astray from the Path (i.e. even worse than cattle)”
[al-Furqaan 25:44]
With regard to smokers or 
    other sinners leading the prayer: such people should not be appointed as 
    imams, rather what is prescribed is to choose the best of the Muslims to 
    lead the prayers, those who are known for their religious commitment and 
    righteousness, because leading the prayers is something important. Hence the 
    Prophet  (peace and blessings of Allaah be upon him) said: “Let the 
    people be led in prayer by the one who has most knowledge of the Qur’aan. If 
    they are equal in terms of knowledge of the Qur’aan, then let them be led by 
    the one who has most knowledge of the Sunnah. If they are equal in terms of 
    knowledge of the Sunnah, then let them be led by the one who migrated first. 
    If they are equal in terms of migration, then let them be led by the one who 
    become Muslim first.” Narrated by Muslim in his Saheeh. In 
    al-Saheehayn it is also narrated that the Prophet  (peace and 
    blessings of Allaah be upon him) said to Maalik ibn al-Huwayrith and his 
    companions: “When the time for prayer comes, let one of you give the call to 
    prayer and let the oldest of you lead you in prayer.” 
The scholars differed as to 
    whether it is valid for a sinner to lead the prayer and whether prayers 
    offered behind him are valid. Some of them said that a prayer offered behind 
    him is not valid, because his religious commitment is weak and his faith is 
    lacking. Other scholars said that it is valid for him to lead the prayer and 
    prayers offered behind him are valid, because he is a Muslim whose prayer is 
    valid in and of itself, so prayers offered behind him are valid, because 
    many of the Sahaabah prayed behind some rulers who were known to be 
    wrongdoers and evildoers, such as Ibn ‘Umar (may Allaah be pleased with him) 
    who prayed behind al-Hajjaaj who was one of the greatest wrongdoers. This is 
    the correct view, which is that his prayers are valid, as are the prayers of 
    those who pray behind him. But he should not be appointed as an imam when it 
    is possible to appoint someone else who is good and righteous. 
Fataawa al-Shaykh Ibn 
    Baaz (12/123-127). 
The Shaykh (may Allaah have 
    mercy on him) was also asked: 
What is the ruling on 
    praying behind sinners such as those who shave their beards or smoke? 
He replied: 
The scholars differed 
    concerning this issue. Some are of the view that it is not valid to pray 
    behind a sinner, because he is weak in faith and not trustworthy. But a 
    large number of scholars are of the view that it is valid, but those who are 
    in authority should not appoint sinners to lead the people in prayer when 
    there are other people available. This is the correct view, because he is a 
    Muslim who knows that prayer is obligatory upon him and he does it on that 
    basis. So it is valid to pray behind him. The evidence for that is the 
    report in the saheeh hadeeth, that the Prophet  (peace and blessings of 
    Allaah be upon him) said concerning prayer behind immoral rulers: “They lead 
    you in prayer and if they do good then it will be for you and for them, but 
    if they do evil then it will be for you and against them.” Narrated by 
    al-Bukhaari in al-Adhaan (662). And there are other ahaadeeth in 
    which the Prophet  (peace and blessings of Allaah be upon him) said 
    something similar. And some of the Sahaabah prayed behind al-Hajjaaj even 
    though he was among the most evil of people, and because prayer in 
    congregation is essential, so the believer should be keen to do it and to 
    pray in congregation regularly even if the imam is an evildoer. But if it is 
    possible to pray behind an imam of good character, then that is better and 
    is preferable, and is more on the safe side with regard to religious 
    commitment.  
Fataawa al-Shaykh Ibn 
    Baaz (6/400). 
Shaykh Muhammad ibn Saalih 
    al-‘Uthaymeen (may Allaah have mercy on him) said: 
Prayer offered behind a 
    smoker is valid, and the prayer of the smoker is valid. If a person’s prayer 
    is valid then it is valid for him to lead the prayer, because the point is 
    that he is leading you in prayer and that can only be valid if his own 
    prayer is valid. Hence if you find someone who smokes or shaves his beard or 
    deals in riba etc, there is nothing wrong with your praying with him, and 
    your prayer is valid. 
Majmoo’ Fataawa 
    al-Shaykh Ibn ‘Uthaymeen (15/question no. 1003) 
Ends.