“Liars are always most disposed to swear.”

Source: The Prisoner of Heaven

Source: 1990s, Palimpsest : A Memoir (1995), Ch. 18: To Do Well What Should Not Be Done at All, p. 311

Un menteur est toujours prodigue de serments.
Clariste, act III, scene v.
Le Menteur (The Liar) (1643)

No. 2.
The Biglow Papers (1848–1866), Series II (1866)

1860s, Our Composite Nationality (1869)
Context: The next objection to the Chinese is that he cannot be induced to swear by the Bible. This is to me one of his best recommendations. The American people will swear by any thing in the heaven above or the earth beneath. We are a nation of swearers. We swear by a book whose most authoritative command is to swear not at all. It is not of so much importance what a man swears by, as what he swears to, and if the Chinaman is so true to his convictions that he cannot be tempted or even coerced into so popular a custom as swearing by the Bible, he gives good evidence of his integrity and of his veracity. Let the Chinaman come; he will help to augment the national wealth; he will help to develop our boundless resources; he will help to pay off our national debt; he will help to lighten the burden of our national taxation; he will give us the benefit of his skill as manufacturer and as a tiller of the soil, in which he is unsurpassed.