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

Shakespeare - never doubt I love - wist_info quote

William Shakespeare (1564-1616) English dramatist and poet
Hamlet, Act 2, sc. 2, l. 124ff [Hamlet] (c. 1600)

A letter from Hamlet to Ophelia, read by Polonius.