'According to the Law' in the Bible

Now, O king, establish the injunction and sign the document so that it may not be changed, according to the law of the Medes and Persians, which may not be revoked.”

Then they approached and spoke before the king about the king’s injunction, “Did you not sign an injunction that any man who makes a petition to any god or man besides you, O king, for thirty days, is to be cast into the lions’ den?” The king replied, “The statement is true, according to the law of the Medes and Persians, which may not be revoked.”