15 Then these men assembled together to the king, and said to the king, “Know, O king, that it is a law of the Medes and Persians, that no decree nor statute which the king establishes may be changed.”
Daniel 6:15 Cross References - WEB
Esther 8:8
8 Write also to the Jews, as it pleases you, in the king’s name, and seal it with the king’s ring; for the writing which is written in the king’s name, and sealed with the king’s ring, may not be reversed by any man.”
Psalms 94:20-21
Daniel 6:8
8 Now, O king, establish the decree, and sign the writing, that it not be changed, according to the law of the Medes and Persians, which doesn’t alter.”
Daniel 6:12
12 Then they came near, and spoke before the king concerning the king’s decree: “Haven’t you signed a decree that every man who makes a 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, “This thing is true, according to the law of the Medes and Persians, which doesn’t alter.”