A man who parades his piety is one who, under an atheist king, would be an atheist.

[Un dévot est celui qui, sous un roi athée, serait athée.]

Jean de La Bruyère (1645-1696) French essayist, moralist

The Characters [Les Caractères], ch. 13 “Of the Fashion [De la Mode],” § 21 (13.21) (1688)
    (Source)

La Bruyère notes in the original this refers to a "faux dévot."

(Source (French)). Alternate translations:

An Hypocrite is one that will be an Atheist under a King that is so.
[Bullord ed. (1696)]

A Devote is one, that under a King who was an Atheist, would be a Devote.
[Curll ed. (1713)]

A Devoto is one, that under an atheistical King wouild be an Atheist.
[Browne ed. (1752)]

A pious person is one who, under an atheistical king, would be an atheist.
[tr. Van Laun (1885)]

A pious hypocrite is one who, under an atheistic king, would be an atheist.
[tr. Stewart (1970)]