Sometimes I stay away from work to do things I need to do, without his permission, but I record it as if I was present at work, as he has withheld many of my rights from me. Is that permissible? And what does repentance entail?.
It is permissible to work for a kaafir or mushrik, so long as one does not approve of anything of his disbelief or sins. So it is obligatory to object to him if he makes fun of Islam or Muslims. It is also obligatory to adhere to Islamic guidelines such as not regarding him as a friend, not being the first one to greet, and so on. It is better to work for a Muslim who fears Allah.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: There is someone who works with the kuffaar; what advice can you give him?
He replied: We advise this brother who works with the kuffaar to seek work where there are none of the enemies of Allah and His Messenger who follow a religion other than Islam. If this is possible, then this is what he should do. If it is not possible then there is nothing wrong with it, because he is doing his job and they are doing theirs, but that is on condition that there be no fondness or love or feelings of friendship towards them in his heart, and that he adhere to the rulings of Islam concerning greeting them, returning their greetings, and so on. Also, he should not attend their funerals or celebrations, and he should not congratulate them on their festivals.
End quote from Fataawa ash-Shaykh Ibn ‘Uthaymeen, 3/39
It is not permissible to stay away from work whilst recording it as if one were present, because that is lying. What you have to do is strive to attain your rights in proper, legitimate ways.
What you have to do is render back trusts that he has entrusted to you, and fulfil the conditions that he stipulated for you in your work with him.
And Allah knows best.