“Live among men as if God beheld you; speak with God as if men were listening.”
sic vive cum hominibus tamquam deus videat, si loquere cum deo tamquam homines audiant.
Seneca the Younger (-4–65 BC) Roman Stoic philosopher, statesman, and dramatist
Source: Epistulae Morales ad Lucilium (Moral Letters to Lucilius), Letter X: On living to oneself, Line 5.