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."