Wonderful, thanks! Recording the quote for posterity:
Nothing can be soundly understood
If daylight itself needs proof.
(Imam al-Haddad, The Sublime Treasures)
Don't know the original quote but strongly reminds me of GE Moore's response to skeptical arguments: 'Here is one hand' (wiki)
"At the foundation of well-founded belief lies belief that is not founded." (Wittgenstein, On Certainty) And more precisely: "The questions we raise and our doubts depend on the fact that some propositions are exempt from doubt, are as it were like hinges on which those turn." Hayek touches this obliquely - the error of demanding explicit justification for everything, including the knowledge that makes justification possible. To demand a proof-chain all the way down is to misunderstand how knowledge actually works. Albert's Münchhausen Trilemma is the critical-rationalist statement of the same problem: any demand for complete justification ends in infinite regress, circularity, or arbitrary stopping points. Some things are not the object of proof - they are the condition of proof.
I remember reading a quote, I think from the Buddhist or some other Eastern tradition, about how if you've argued yourself into believing the Sun doesn't exist, you've gone horribly wrong. It went something like "Nothing can be known, if even the Sun requires proof". I think I read it either on LessWrong or on gwern.net several years ago, but for the life of me I can't find it. I remember it being phrased more poetically than prosaically.
Does anyone know what quote I'm referring to, and where to find it?