Don't look a gift horse in the mouth
Description
Do not unappreciatively question a gift or handout too closely.
Etymology
Since horses' teeth change over time, inspecting their teeth is a way of gauging age. However, doing such a check would be a sign of mistrust towards the giver.
From Middle English texts for “given horse”:
No man ought to looke a geuen hors in the mouth. — John Heywood, 1546.
The substitution of gift for given occurred in 1663 in Butler's Hudibras, because the iambic tetrameter required a shortening:
He ne’er consider'd it, as loth
To look a Gift-horse in the mouth.
Although uncertain, the origin can be traced even further to St. Jerome's Latin Equi dentes inspicere donati., from the Preface to the Commentaries of the Letter to the Ephesians, circa AD 400, where it is denoted as a "common proverb" ("vulgare proverbium"). In: Patrologia Latina Volume 26, S. Eusebii Hieronymi, Stridonensis Presbyteri, Commentariorum In Epistolam Ad Ephesios Libri Tres, 537-538.
