For Justice is one; it binds all human society, and is based on one Law, which is right reason applied to command and prohibition. Whoever knows not this Law, whether it has been recorded in writing anywhere or not, is without Justice.

[Est enim unum ius quo deuincta est hominum societas et quod lex constituit una, quae lex est recta ratio imperandi atque prohibendi. Quam qui ignorat, is est iniustus, siue est illa scripta uspiam siue nusquam.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

De Legibus [On the Laws], Book 1, ch. 15 (1.15) / sec. 42 [Marcus] (c. 51 BC) [tr. Keyes (1928)]
    (Source)

(Source (Latin)). Alternate translations:

There can be but one essential justice, which cements society, and one law which establishes this justice. This law is right reason, which is the true rule of all commandments and prohibitions. Whoever neglects this law, whether written or unwritten, is necessarily unjust and wicked.
[tr. Barham (1842)]

For there is but one essential justice which cements society, and one law which establishes this justice. This law is right reason, which is the true rule of all commandments and prohibitions. Whoever neglects this law, whether written or unwritten, is necessarily unjust and wicked.
[tr. Barham/Yonge (1878)]

There is one, single, justice. It binds together human society and has been established by one, single, law. That law is right reason in commanding and forbidding. A man who does not acknowledge this law is unjust, whether it has been written down anywhere or not.
[tr. Rudd (1998)]

There is only one justice, which constitutes the bond among humans, and which was established by the one law, which is right reason in commands and prohibitions. The person who does not know it is unjust, whether the law has been written anywhere or not.
[tr. Zetzel (1999)]

Right is uniform; human fellowship has been bound by it, and one law has established it; that law is correct reason in commanding and prohibiting. He who is ignorant of it is unjust, whether it has been written somewhere or nowhere.
[tr. Fott (2013)]