Is it permissible for an employee who works in an appliance repair shop and receives a monthly salary to tell the shop owner that he bought a spare part for a device for a certain amount and take this amount for himself, while he actually repaired the original part and did not buy a new one?

Lying, deception, and unlawfully consuming people's wealth are impermissible, for the Prophet, peace and blessings be upon him, said: "Indeed, lying leads to wickedness, and wickedness leads to the Hellfire," and "Whoever cheats is not one of us," and "Treachery, deceit, and betrayal are in the Hellfire."

Therefore, if you lied to the device owner that you bought a part and took its price from him, you must return the thousand to him. If you cannot reach him, then give it as charity on his behalf. He then has the choice between approving the charity or taking his right.

However, if you agreed with him to repair the device for two thousand and concealed a thousand from him, you must return the amount to him, or seek his forgiveness by informing him of what you did. If he permits you, then there is no harm; otherwise, it is obligatory to return it.