Does one sin who teaches employees of a tobacco company after having entered into a contract before knowing that they work for this company, and what is the ruling on the money earned from that?

It is forbidden to smoke, manufacture, sell, or buy tobacco, and to assist in any of these, due to the severe harm it causes, and due to the generality of Allah's saying: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression) [Al-Ma'idah 5:2], and the Prophet, peace and blessings be upon him, said: (There should be neither harm nor reciprocating harm), and his saying: (Indeed, when Allah forbids a thing, He also forbids its price).

Therefore, it is not permissible to train workers in a tobacco company, as it is assisting in sin, and the money earned from it is unlawful. It is obligatory to repent to Allah and dispose of this money by giving it to the poor and needy, or for general Muslim welfare, and it should not be returned to the company, so that the company does not combine both compensation and the compensated.