What is the ruling on one who forged a PhD certificate, and is working and receiving a higher salary based on it, and heads a department and supervises PhD theses, and what are the Shariah implications of this, and is it sufficient for him to donate part of his salary in charity?

The fundamental principle is that whoever possesses the competence for a particular task is permitted to perform it, even if they do not hold a certificate. A license from a shaykh is not a prerequisite for undertaking teaching and instruction. Therefore, whoever knows themselves to be qualified is allowed to do so, even if no one has authorized them. However, people have conventionally adopted the concept of a license as a certificate to authenticate a person's qualification.

If the employer requires a specific certificate, it is not permissible to work with a forged certificate due to the deception involved. However, if competence is the primary requirement and the certificate serves a symbolic role, then there is no harm in working with that certificate for someone who possesses the competence.

Accordingly, if the employer requires a certificate, they must be informed of the true nature of the certificate. If they accept continued employment, then good; otherwise, the job should be left. The salary is permissible if the work is performed competently, because it is in exchange for the effort expended.