TARTUFFE: Your scruple, then, is easy to allay:
Our secret will be safe with us alone,
And there’s no evil if the thing’s not known.
The one offense lies in the public shame,
And secret sin is sin only in name.

[Enfin votre scrupule est facile à détruire.
Vous êtes assurée ici d’un plein secret,
Et le mal n’est jamais que dans l’éclat qu’on fait.
Le scandale du monde est ce qui fait l’offense,
Et ce n’est pas pécher que pécher en silence]

Molière (1622-1673) French playwright, actor [stage name for Jean-Baptiste Poquelin]

Tartuffe, or the Hypocrite [Le Tartuffe, ou L’Imposteur], Act 4, sc. 5 (1669) [tr. Frame (1967)]
    (Source)

The ostensibly pious Tartuffe trying to seduce Elmire.

(Source (French)). Other translations:

In short your Scruple, Madam, is easily overcome. You are sure of its being an inviolable Secret here, and the Harm never consists in any thing but the Noise one makes; the Scandal of the World is what makes the Offence; and Sinning in private is no Sinning at all.
[tr. Clitandre (1672)]

In short, your scruples, Madam, are easily overcome. You may be sure of the secret being kept, and there is no harm done unless the thing is bruited about. The scandal which it causes constitutes the offence, and sinning in secret is no sinning at all.
[tr. Van Laun (1876)]

In short, your scruples, madam, are easy to remove. You are sure of an inviolable secrecy with me, and it is only publicity which makes the wrong. The scandal is what constitutes the offence, and to sin in secret is not to sin at all.
[tr. Wall (1879)]

In short, madame, your scruple is easily overcome. You are sure of absolute secrecy here, and the evil only consists in the noise that is made about it ; the world’s scandal makes the offence, and to sin in private is no sin at all.
[tr. Mathew (1890), 4.4]

In short your scruple is easily overcome. You may be sure the secret will be well kept here, and no harm is done unless the thing is noised abroad. The scandal of the world is what makes the offence, and to sin in secret is not to sin at all.
[tr. Waller (1903)]

In any case, your scruple's easily
Removed. With me you're sure of secrecy,
And there's no harm unless a thing is known.
The public scandal is what brings offence,
And secret sinning is not sin at all.
[tr. Page (1909)]

Well, anyway, I can dispel your scruples.
You are assured that I will keep the secret.
Evil does not exist until it's published;
It's worldly scandal that creates the offense;
And sin in silence is not sin at all.
[tr. Bishop (1957)]

If you're still troubled, think of things this way:
No one shall know our joys, save us alone,
And there's no evil till the act is known;
It's scandal, Madam, which makes it an offense,
And it's no sin to sin in confidence.
[tr. Wilbur (1963)]

Well, Moses couldn't matter less,
The ten commandments don't apply,
There's no one here -- just you and I,
It's scandal that creates the sin,
This won't get out, so let's begin.
[tr. Bolt (2002)]

In the end, I assure you, it's easy to dismiss your scruples. I promise complete secrecy; only when others make a fuss can there be any harm. Something is scandalous only when it is known; sin that no one knows is no sin.
[tr. Steiner (2008)]

Look, your scruples are easily dealt with:
You can be quite certain that it will remain secret,
And the sin is only ever in the exposure;
A silent sin is not a sin at all.
[tr. Campbell (2013)]