Is it permissible to work in a foreign country after graduation and before receiving the diploma, given a prior condition for students not to work part-time, and is the money earned from this work unlawful?

The basic principle is the obligation to adhere to the condition agreed upon in the contract, because the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." Violating a condition does not prohibit earnings for work that is in itself permissible; rather, accountability is only for violating the condition. It is permissible to work during the period of waiting for the certificate after completing studies, unless the university administration prohibits it.