After working with a company for 3 weeks, I discovered that it was cheating on the work, by using a trick to raise certain quantities to make it seem like the task was successfully completed.At this time I was not involved in the cheating part. I was doing maintenance work, carrying things, and installing pipes, but after 7 weeks my boss began to involve me in this part, and cheating became my main task. I tried to avoid this by doing other tasks, but that didn't work.During my time with this company, I saved some money. I left after working with them for 3 months. My question to you may God reward you for the good, can I benefit from this money? I wanna invest it in a small project.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Cheating is forbidden, and it was your duty to refrain from engaging in dishonesty with the company, even if it led to you leaving the job. If you assisted the company in cheating, it is incumbent upon you to sincerely repent. As for the ruling on your salary in this company, it depends on the nature of the work. Since you mentioned that cheating has become your primary task, the entire or a significant portion of the salary is now in exchange for cheating, making it forbidden.

However, regarding the period before this or any earnings related to legitimate work, it is halal (lawful). You should remove the unlawful portion of the salary and use it for charitable purposes unless you are in a state of poverty. In that case, you are allowed to take from it according to your needs. If you are poor, it is permissible for you to use that money for a project that allows you to earn a living.

When Sheikh al-Islam Ibn Taymiyyah was asked about a singer who acquired a significant amount of wealth in her ignorance but then repented, part of his response was: “This wealth is not permissible for her, but it can be spent in the interests of the Muslims. If she repents from this wrongdoing and this unlawful gain, and they are poor, it is permissible to allocate from this wealth to them according to their needs. If they are capable of trading or engaging in a craft such as weaving and spinning, they are given an amount that serves as capital for them to start a business.”

Allah knows best.