The sources of a constitution are:-

Legislature,Legal instrument,Statute and Parliamentary acts
Historical documents
Constitution of other countries
Previous constitutions of the country
Opinions,writings and commentaries of eminent legal experts and political thinkers, government authorities and committees
Usages,Principles,Norms,Habits,Customs,Convention,Practices,Traditions,Rule of actions applicable to government- Common Law {Established and accepted patterns of behaviour of governance}

Judicial decisions,Commentary by judiciary, Judges made maxims- Case Laws {Judge made laws}

Decisions of constitutional assembly
Parliamentary standing orders
Legal doctrines and concepts
Theory of judicial precedent
Religious legal texts
Equity,Justice and Good Conscience