It is not permissible to smoke. There is financial loss as well as health damage. The sin of knowingly harming one's life and property. In addition, bad breath hurts others , which is a separate sin. It is said in the hadith , “Whoever believes in Allah and the Last Day, then he will not be guided . ” " Whoever believes in Allah and the Last Day, let him not harm his neighbor." (Sahih Bukhari 7/27) On the contrary, it is makrooh to enter the mosque in this condition. It is also forbidden in the hadith to enter the mosque by eating raw onion-garlic which is much less foul smelling than smoking. Prophet (peace be upon him) said , من أكل البصل والثوم والكراث فلا يقربن مسجدنا, فإن الملا يقربن مما يتأذى منه بنو آدم " The person who smells like onions , garlic, and onion, do not come to our mosque , because it does not come to our mosque . The angels suffer just as much as people suffer from bad smells . ” (Sahih Muslim 1/395) If you smoke, it gives off a bad smell. Smells more like onion , garlic. Therefore, it is easy to guess that it will be forbidden to enter the mosque with the strong stench of smoking. But if there is no one better than the smoker or you come and pray behind the smoker, then your prayer will be done. No need to repeat the prayer. (Fatawal Lajnatid Daima 13/56 ; Alfatawash Shariah 10/145 ; Raddul Muhtar 1/61) It is the duty of every believer to take care of this circumcision and keep his teeth and mouth clean.