Daniel 6:15

Then the king, when he heard the saying, was much grieved for Daniel, and he greatly exerted himself for Daniel to deliver him: and he exerted himself till evening to deliver him.

Then those men said to the king, Know, O king, that the law of the Medes and Persians is that we must not change any decree of statue which the king shall make.

Then these men assembled unto the king, and said unto the king, Know, O king, that the law of the Medes and Persians is, That no decree nor statute which the king establisheth may be changed.