What is the ruling on an employee taking a tip that a customer pays directly to him, and what is the ruling on the employer demanding half of it?

Tips given to workers are considered gifts to employees, and it is forbidden to take them without the employer's permission. It is narrated in the Hadith (definition) that the Prophet, peace and blessings be upon him, said: "Gifts to workers are unlawful gains." It is also reported that he reproached a man who was given a gift because of his work, which indicates that it is not permissible to take such gifts except with the employer's permission.