Daniel 6:12 (ESV)

12 Then they came near and said before the king, concerning the injunction, “O king! Did you not sign an injunction, that anyone who makes petition to any god or man within thirty days except to you, O king, shall be cast into the den of lions?” The king answered and said, “The thing stands fast, according to the law of the Medes and Persians, which cannot be revoked.”

Daniel’s enemies are rubbing their hands with glee. Everything has gone as they had hoped. After only one day, they have sufficient evidence against Daniel. Thus, they can confidently appear before Darius, and that is exactly what they do next. They remind the king of the law he had issued. The king confirms that they represent its contents well. It really is an unalterable law, also for the king.