Which of the following is NOT a source of customary international law?

Customary international law is derived from practices and norms that are widely accepted as legally binding by states, which include the consistent and general practice of states accompanied by a belief that such practices are required by law (opinio juris).

Local state statutes do not contribute to customary international law because they are domestic laws that apply only within the jurisdiction of a specific state. They do not reflect the behavior or practices of states on an international level and thus lack the necessary elements of widespread adherence or belief in legal obligation required for a norm to become customary international law.

In contrast, the other options contribute to the formation of customary international law. Decisions from international courts can indicate how international norms are interpreted and applied. State customs and practices reflect the actual behavior of states over time, which can establish norms that are recognized internationally. The published works of legal scholars help to elucidate and analyze these practices and can influence both state behaviors and judicial interpretations of international law.