Jamieson, Fausset and Brown on Daniel 6:9

9. Such a despotic decree is quite explicable by remembering that the king, as the incarnation of Ormuzd, might demand such an act of religious obedience as a test of loyalty. Persecuting laws are always made on false pretenses. Instead of bitter complaints against men, Daniel prays to God. Though having vast business as a ruler of the empire, he finds time to pray thrice a day. Daniel's three companions (Da 3:12), are not alluded to here, nor any other Jew who conscientiously may have disregarded the edict, as the conspirators aimed at Daniel alone (Da 6:5).