“Vile latens virtus.”

Of Adversity
Essays (1625)
Context: The virtue of prosperity, is temperance; the virtue of adversity, is fortitude; which in morals is the more heroical virtue. Prosperity is the blessing of the Old Testament; adversity is the blessing of the New; which carrieth the greater benediction, and the clearer revelation of God's favor. Yet even in the Old Testament, if you listen to David's harp, you shall hear as many hearse-like airs as carols; and the pencil of the Holy Ghost hath labored more in describing the afflictions of Job, than the felicities of Solomon. Prosperity is not without many fears and distastes; and adversity is not without comforts and hopes.

Augustus William Hare and Julius Charles Hare Guesses at Truth (London: Macmillan, ([1827-48] 1867) p. 1.
Misattributed

"Canon Law: Ecclesiastical Ministry" (1771)
Questions sur l'Encyclopédie (1770–1774)
Context: Virtue supposes liberty, as the carrying of a burden supposes active force. Under coercion there is no virtue, and without virtue there is no religion. Make a slave of me, and I shall be no better for it. Even the sovereign has no right to use coercion to lead men to religion, which by its nature supposes choice and liberty. My thought is no more subject to authority than is sickness or health.

(6 August 1796)
1750s, Diaries (1750s-1790s)
Context: Omnium rerum domina, virtus. Virtue is the mistress of all things. Virtue is the master of all things. Therefore a nation that should never do wrong must necessarily govern the world. The might of virtue, the power of virtue, is not a very common topic, not so common as it should be.

[2013, From the Divine to the Human, World Wisdom, 70, 978-1-936597-32-1]
Spiritual path, Virtue

Speech to the National Convention, (5 February 1794), as quoted in The Bolshevik Revolution, 1917-1923, Vol. 1 (1951) by Edward Hallett Carr, p. 154
Variant translations:
The attribute of popular government in a revolution is at one and the same time virtue and terror. Terror without virtue is fatal; virtue without terror is impotent. The terror is nothing but justice, prompt, severe, inflexible; it is thus an emanation of virtue.
As quoted in Red Star Over Southern Africa (1988) by Morgan Norval, p. xvi
If the mainspring of popular government in peace time is virtue, its resource during a revolution is at one and the same time virtue and terror; virtue, without which terror is merely terrible; terror, without which virtue is simply powerless.
As quoted in Rousseau, Robespierre and English Romanticism (1999) by Gregory Dart
Terror is nothing other than justice, prompt, severe, inflexible; it is therefore an emanation of virtue; it is not so much a special principle as it is a consequence of the general principle of democracy applied to our country's most urgent needs.
Original French: La terreur n'est autre chose que la justice prompte, sévère, inflexible; elle est donc une émanation de la vertu ; elle est moins un principe particulier, qu’une conséquence du principe général de la démocratie, appliqué aux plus pressants besoins de la patrie.
From Sur les principes de morale politique http://www.royet.org/nea1789-1794/archives/discours/robespierre_principes_morale_politique_05_02_94.htm

1840s, Essays: First Series (1841), Friendship
Variant: The only way to have a friend is to be one.

Dialogue on the Soul and the Resurrection, Patrologia Graeca 46.101-105

Source: The Analects, Chapter IV