Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
Smoking cigarettes does not invalidate ablution (wudu). Therefore, a smoker is not required to repeat their wudu because of smoking, since smoking is not one of the acts that nullify ablution according to Islamic law.
Is it permissible to enter the mosque after smoking?
If a smoker wishes to enter the mosque, they should remove the smell of smoke from their mouth by rinsing it, brushing their teeth, using a miswak, or any similar means that eliminates the odor. This is because the smell of smoke is unpleasant and harms both the worshippers and the angels.
The Prophet ﷺ prohibited those who had eaten garlic or onions from entering the mosque until their odor had disappeared. The smell of cigarettes is even more deserving of avoidance because of the harm it causes.
What is the ruling on smoking?
According to the majority of contemporary scholars, smoking is prohibited (haram) because of its proven severe harm to one's health and wealth, as well as the harm it causes to others. Allah, the Exalted, says:
"And do not kill yourselves. Indeed, Allah is ever Merciful to you."
(Qur'an 4:29)
And He also says:
"And do not throw yourselves into destruction with your own hands."
(Qur'an 2:195)
Therefore, every Muslim should strive to quit smoking and sincerely repent to Allah.
What is the ruling on selling cigarettes?
Selling cigarettes and trading in them is also prohibited because they are harmful and impure. It is not permissible to assist in spreading them or to earn money from their sale.
Summary
Smoking does not invalidate wudu, but a smoker should remove the smell of smoke before entering the mosque so as not to harm the worshippers or the angels. Smoking and selling cigarettes are both prohibited because of the great harm they cause. Every Muslim should hasten to repent and quit smoking.
And Allah knows best.