“Separation has this lofty meaning:
if love lasts years, if but a day it takes,
love's just a dream and we're a moment dreaming,
and whether early, whether late the waking,
the time must finally arrive when we awake.”

Source: The Lover's Dictionary

Source: Short fiction, The Martian and the Moron (1949), p. 44

Variants:
Novalis (1829)
Variant: We are near awakening when we dream that we dream.
Source: Novalis: Philosophical Writings

Homecoming saga, The Ships Of Earth (1994)

The third and fourth sentences are a paraphrase of a sentence by G. K. Chesterton: "I do not believe in a fate that falls on men however they act; but I do believe in a fate that falls on them unless they act." Generally Speaking, "On Holland' (1928).
1980s, First term of office (1981–1985), First Inaugural address (1981)
Context: It is time for us to realize that we're too great a nation to limit ourselves to small dreams. We're not, as some would have us believe, doomed to an inevitable decline. I do not believe in a fate that will fall on us no matter what we do. I do believe in a fate that will fall on us if we do nothing. So, with all the creative energy at our command, let us begin an era of national renewal. Let us renew our determination, our courage, and our strength. And let us renew our faith and our hope. We have every right to dream heroic dreams. Those who say that we're in a time when there are no heroes, they just don't know where to look.

In Heaven There Is No Heat
Cavalry of Light (2005)

Mas, sea verdad o sueño,
obrar bien es lo que importa.
Si fuere verdad, por serlo;
si no, por ganar amigos
para cuando despertemos.
Segismundo, Act III, l. 236.
La vida es sueño (Life is a Dream)