I refer to his passage from Cicero's "Republic" very often to contrast it as essentially the opposite of Epicurus' view of justice, but I always have a hard time finding it when I need it. This post is just to provide some links and clips to the key passage:
Attalus: {22.} [33] L . . . True law is right reason in agreement with nature , it is of universal application, unchanging and everlasting; it summons to duty by its commands, and averts from wrongdoing by its prohibitions. And it does not lay its commands or prohibitions upon good men in vain, though neither have any effect on the wicked. It is a sin to try to alter this law, nor is it allowable to attempt to repeal any part of it, and it is impossible to abolish it entirely. We cannot be freed from its obligations by senate or people, and we need not look outside ourselves for an expounder or interpreter of it. And there will not be different laws at Rome and at Athens, or different laws now and in the future, but one eternal and unchangeable law will be valid for all nations and all times, and there will be one master and ruler, that is, God, over us all, for he is the author of this law, its promulgator, and its enforcing judge. Whoever is disobedient is fleeing from himself and denying his human nature, and by reason of this very fact he will suffer the worst penalties, even if he escapes what is commonly considered punishment. . . .
Loeb Edition:
Note: I am not able to find a good copy of this for free and online. If someone has a link please let me know.
Yonge: (link to this version at archive.org)