“[The atheist's] faith is much greater than mine. I could never for a moment believe that all these things happened by chance. Never in a million years. But the believing atheist does, and he amazingly looks down intellectually on those that maintain that all this incredible creation wasn't an act of an incredible creator.”

Source: 2010s, 2011, Mortality (2012), p. 91.

Source: Down and out in Paris and London (1933), Ch. 30
Source: Down and Out in Paris and London
Context: He was an embittered atheist (the sort of atheist who does not so much disbelieve in God as personally dislike Him), and took a sort of pleasure in thinking that human affairs would never improve. Sometimes, he said, when sleeping on the Embankment, it had consoled him to look up at Mars or Jupiter and think that there were probably Embankment sleepers there. He had a curious theory about this. Life on earth, he said, is harsh because the planet is poor in the necessities of existence. Mars, with its cold climate and scanty water, must be far poorer, and life correspondingly harsher. Whereas on earth you are merely imprisoned for stealing sixpence, on Mars you are probably boiled alive. This thought cheered Bozo, I do not know why. He was a very exceptional man.

Lurker's Guide to Babylon 5 : "Passing Through Gethsemane : jms speaks" (13 July (2004) http://www.midwinter.com/lurk/countries/us/guide/048.html.
Context: As an atheist, I believe that all life is unspeakably precious, because it’s only here for a brief moment, a flare against the dark, and then it’s gone forever. No afterlives, no second chances, no backsies. So there can be nothing crueler than the abuse, destruction or wanton taking of a life. It is a crime no less than burning the Mona Lisa, for there is always just one of each. So I cannot forgive.

Variant: I can believe anything provided it is incredible.
Source: The Picture of Dorian Gray

Last Notebook (1942) p. 137
First and Last Notebooks (1970)
Context: In order to obey God, one must receive his commands. How did it happen that I received them in adolescence, while I was professing atheism? To believe that the desire for good is always fulfilled — that is faith, and whoever has it is not an atheist.

From Peter Engel, "An Interview With Stanislaw Lem": The Missouri Review, Volume VII, Number 2 (1984) http://www.missourireview.org/index.php?genre=Interviews&title=An+Interview+with+Stanislaw+Lem

As quoted in Against the Faith (1985) by Jim Herrick, p. 75
Variant translation: It is very important not to mistake hemlock for parsley, but to believe or not believe in God is not important at all.

A Week on the Concord and Merrimack Rivers http://www.gutenberg.org/dirs/etext03/7cncd10.txt (1849), Sunday