Daniel 6:14-15

14And the king, when he heard these words, was greatly displeased with himself, and set his heart on Daniel to deliver him; and he labored till the going down of the sun to deliver him.

15Then these men approached the king, and said to the king, “Know, O king, that it is the law of the Medes and Persians that no decree or statute which the king establishes may be changed.”