Read the following scenario and answer the question that follows:

You are a candidate attorney working at a community legal aid center. One afternoon, Mr Khumalo approaches you for legal advice. He shows you a letter from his employer which indicates that he has been dismissed with immediate effect, with no reasons being stated in the letter. You are tasked with finding the relevant sources of law which will assist your principal attorney in preparing her case. During your research, you find various South African sources of law.

Which one of the following sources of law is NOT an authoritative source of law?