Is praying behind a smoking imam forbidden or permissible?

Smoking is forbidden and harmful, as the Prophet, peace and blessings be upon him, said: "There should be no harm nor reciprocating harm." A smoker is a transgressor (fasiq), and prayer behind a transgressor is valid. However, it is preferable to pray behind someone else and to shun him so that he may be deterred, unless this leads to abandoning congregational prayer, in which case it is not permissible. Therefore, it is obligatory for one who has no excuse to attend congregational prayer, even if it is behind a transgressor. Indeed, the Companions prayed behind Al-Hajjaj ibn Yusuf Al-Thaqafi despite his transgression.