He that has light within his own clear breast
May sit i’th center, and enjoy bright day,
But he that hides a dark soul, and foul thoughts
Benighted walks under the mid-day sun;
Himself is his own dungeon.

John Milton (1608-1674) English poet

A Mask Presented at Ludlow Castle, ll. 380-84 (1634)
    (Source)

The title was changed to Comus for the 1737 stage version.