Make my breast
Transparent as pure crystal, that the world,
Jealous of me, may see the foulest thought
My heart holds.

Act III, scene 2, line 144. These lines are used almost unaltered ("holds" becoming "does hold") by George Villiers, 2nd Duke of Buckingham in Act III, scene ii of his The Restauration, an adaptation of Philaster. They appear with an attribution to Buckingham in many 19th century collections of quotations, e.g. Henry George Bohn A Dictionary of Quotations from the English Poets (1867) p. 63, and hence also on several quotation websites.