Daniel 6:13-16
English Standard Version
14Then the king, when he heard these words, was much distressed and set his mind to deliver Daniel. And he labored till the sun went down to rescue him.
15Then these men came by agreement to the king and said to the king, "Know, O king, that it is a law of the Medes and Persians that no injunction or ordinance that the king establishes can be changed."