Doubt;

Doubt thou, the Starres are fire,
Doubt, that the Sunne doth moue:
Doubt Truth to be a Lier,
But neuer Doubt, I loue.

from Hamlet Act 2 scene 2, as it appears in the 1623 First Folio. In modern form:

Doubt thou the stars are fire,
Doubt that the sun doth move,
Doubt truth to be a liar,
But never doubt I love.

by William Shakespeare (1564-1616)