You Don't Deserve This Money
Question :
A colleague and I were commissioned to do a job somewhere for a period of four days. I didn't go with him, though, and I later received compensation for that commission. Can I spend that money or not? If I can't spend it on myself, can I spend it on office supplies I need for work?
Answer:
It is incumbent upon you to return that money because you didn't do what you have been asked to do. If that is not possible, you must spend it on a good cause, such as charity for the poor. You must ask Allâh Almighty to forgive you, and you must repent and not repeat that act again.
Source:
Ibn Baz
Fatawa Islamiyah, Vol. 8 Pages 101-102