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?
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”
“Verily, Allaah is Ever All‑Knowing, All‑Wise”
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)]”
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)”
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”
“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)”
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?
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)