Don't Accept the Extra Money
Question :
I work for a maintenance company and I receive a specific monthly salary for that work. Sometimes, though, I go to people's houses to fix something, and the owners insist on giving me a tip for my service. I refuse them despite their continued entreaties. What should I do?
Answer:
Prudence dictates that you should not accept it from them because the Messenger of Allah sent a man named Abdullah bin Al-Lutaybah to collect charity. When he returned with the charity, he said, "This is for you, and this was a gift for me." The Prophet ﷺ delivered a sermon and rebuked this act by saying,
"Should he not have sat in the home of his father or the home of his mother to see if he would get a gift or not."
This expression suggests a warning against taking gifts for workers, for if you remained in your home then these people would not have given you any gift. What is safer and more careful, then, is not to accept anything other than your salary. And Allah Almighty knows best.
Source:
Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 8 Pages 105-106