“The only law to which we can give our obedience is the one of which we are convinced. And this way to act cannot be alleged to be egocentric or disorderly. First of all it is easy to realize that everybody really acts like this, that is, he does not obey laws to which the doors of his conscience have not been willingly opened. But the difference lies in that some choose an authority, and from then onwards are prepared to obey all its commands. Others instead prefer to often re-examine the reasons for these prescriptions, and do not entrust anybody with the keys of their own conscience. This does not mean that they will want to undertake a deep study of every law, every regulation, but the fact is that they do not recognize even their country’s government or their society’s president as an absolute authority. This second way will certainly be more tiring, but it is certain that the first will be more dangerous, because it diseducates people and harms those who exercise power and those who are governed.”

In the Trial of Aaron Burr, August 1807

Captain Francis McCullagh, "The Bolshevik Persecution of Christianity," Dutton and Company, 1924, page 192.
Adressing the court during his political show trial in 1923.

Perelandra (1943)

in Aquinas: Selected Political Writings (Basil Blackwell: 1974), p. 183
Commentary on the Sentences of Peter Lombard

Letter to the Lord Chancellor Lord Loughborough (c. 17 March 1796), quoted in R. B. McDowell (ed.), The Correspondence of Edmund Burke, Volume VIII: September 1794–April 1796 (Cambridge University Press, 1969), p. 432
1790s

"Passages from the life of a philosopher", The Belief In The Creator From His Works, p. 402
Passages from the Life of a Philosopher (1864)
Context: In the works of the Creator ever open to our examination, we possess a firm basis on which to raise the superstructure of an enlightened creed. The more man inquires into the laws which regulate the material universe, the more he is convinced that all its varied forms arise from the action of a few simple principles. These principles themselves converge, with accelerating force, towards some still more comprehensive law to which all matter seems to be submitted. Simple as that law may possibly be, it must be remembered that it is only one amongst an infinite number of simple laws: that each of these laws has consequences at least as extensive as the existing one, and therefore that the Creator who selected the present law must have foreseen the consequences of all other laws. The works of the Creator, ever present to our senses, give a living and perpetual testimony of his power and goodness far surpassing any evidence transmitted through human testimony. The testimony of man becomes fainter at every stage of transmission, whilst each new inquiry into the works of the Almighty gives to us more exalted views of his wisdom, his goodness, and his power.

Ch. 3, Sect. 11 http://www.constitution.org/as/dcg_311.htm
Discourses Concerning Government (1689)

De Re Publica [Of The Republic], Book III Section 22; as translated by Francis Barham
Variant translations:
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.
As translated by Clinton W. Keyes (1928)<!-- ; in De Re Publica, De Legibus (1943), p. 211 -->
Context: There is a true law, a right reason, conformable to nature, universal, unchangeable, eternal, whose commands urge us to duty, and whose prohibitions restrain us from evil. Whether it enjoins or forbids, the good respect its injunctions, and the wicked treat them with indifference. This law cannot be contradicted by any other law, and is not liable either to derogation or abrogation. Neither the senate nor the people can give us any dispensation for not obeying this universal law of justice. It needs no other expositor and interpreter than our own conscience. It is not one thing at Rome and another at Athens; one thing to–day and another to–morrow; but in all times and nations this universal law must for ever reign, eternal and imperishable. It is the sovereign master and emperor of all beings. God himself is its author,—its promulgator,—its enforcer. He who obeys it not, flies from himself, and does violence to the very nature of man. For his crime he must endure the severest penalties hereafter, even if he avoid the usual misfortunes of the present life.

“Thinking for Oneself,” H. Dirks, trans.
Parerga and Paralipomena (1851)