'According to the Law' in the Bible

Now, O king, establish the injunction and sign the document so that it may not be changed, in accordance with the law of the Medes and Persians, which [insures that it] may not be altered or revoked.”

Then they approached and spoke before the king regarding his injunction, “Have you not signed an injunction that anyone who petitions (prays to) any god or man except you, O king, within the designated thirty days, is to be thrown into the den of lions?” The king answered, “The statement is true, in accordance with the law of the Medes and Persians, which may not be altered or revoked.”