Keeping an employee without fixing the salary is not permissible; this makes the transaction invalid. It is necessary to fix the salary at the time of the contract, and in case it is not fixed, he will be entitled to 'Ujrat-e-Misl' (customary wage), meaning he will be entitled to the salary that such a person would receive working elsewhere with the same responsibility. (Derived from: Karobari Masail Aur Un Ka Shar'i Hal, Part 1 / Pg: 93)