Commentary for Daniel 6:16

בֵּאדַ֙יִן֙ גֻּבְרַיָּ֣א אִלֵּ֔ךְ הַרְגִּ֖שׁוּ עַל־מַלְכָּ֑א וְאָמְרִ֣ין לְמַלְכָּ֗א דַּ֤ע מַלְכָּא֙ דִּֽי־דָת֙ לְמָדַ֣י וּפָרַ֔ס דִּֽי־כָל־אֱסָ֥ר וּקְיָ֛ם דִּֽי־מַלְכָּ֥א יְהָקֵ֖ים לָ֥א לְהַשְׁנָיָֽה׃

Then these men came tumultuously unto the king, and said unto the king: ‘Know, O king, that it is a law of the Medes and Persians, that no interdict nor statute which the king establisheth may be changed.’

Rashi on Daniel