“Modernism began in the mid-nineteenth century as a response not only to the restrictions and hypocrisies of everyday life, but also as a reaction to the Enlightenment's emphasis on the rationality of human behavior. …The founders of the Royal Society thought of God as a mathematician who had designed the universe according to logical and mathematical principles. The role of the scientist—the natural philosopher was to… decipher the codebook that God had used in creating the cosmos.”

Source: Beyond Measure (2004), Ch. 1 : An act of desperation

The Age of Insight (2012)

The Evolution of the Physicist's Picture of Nature (1963)
Context: It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it. You may wonder: Why is nature constructed along these lines? One can only answer that our present knowledge seems to show that nature is so constructed. We simply have to accept it. One could perhaps describe the situation by saying that God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe. Our feeble attempts at mathematics enable us to understand a bit of the universe, and as we proceed to develop higher and higher mathematics we can hope to understand the universe better.

Нет бога-творца, но есть космос, производящий солнца, планеты и живых существ. Hет всемогущего бога, но есть вселенная, которая распоряжается судьбой всех небесных тел и их жителей. Нет сынов божьих, но есть зрелые и потому разумные и совершенные сыны космоса. Нет личных богов, но есть избранные правители: планет, солнечных систем, звёздных групп, млечных путей, эфирных островов и всего космоса. Нет Христа, но есть гениальный человек, великий учитель человечества.
from Нет ничего (Мысли безбожника) [There is nothing (Atheist's thoughts)], quoted in Л.В. Шапошникова, Вестники космической эволюции.

Why I Am an Agnostic (1896)

Source: Outsiders: Studies in the Sociology of Deviance (1963), p. 18.

The earliest published source found on google books that attributes this to Euclid is A Mathematical Journey by Stanley Gudder (1994), p. xv http://books.google.com/books?id=UiOxd2-lfGsC&q=%22mathematical+thoughts%22+euclid#search_anchor. However, many earlier works attribute it to Johannes Kepler, the earliest located being in the piece "The Mathematics of Elementary Chemistry" by Principal J. McIntosh of Fowler Union High School in California, which appeared in School Science and Mathematics, Volume VII ( 1907 http://books.google.com/books?id=kAEUAAAAIAAJ&pg=PR3#v=onepage&q&f=false), p. 383 http://books.google.com/books?id=kAEUAAAAIAAJ&pg=PA383#v=onepage&q&f=false. Neither this nor any other source located gives a source in Kepler's writings, however, and in an earlier source, the 1888 Notes and Queries, Vol V., it is attributed on p. 165 http://books.google.com/books?id=0qYXAQAAMAAJ&pg=PA165#v=onepage&q&f=false to Plato. It could possibly be a paraphrase of either or both of the following to comments in Kepler's 1618 book Harmonices Mundi (The Harmony of the World)': "Geometry is one and eternal shining in the mind of God" and "Since geometry is co-eternal with the divine mind before the birth of things, God himself served as his own model in creating the world".
Misattributed

Attributed to Kepler in some sources (though more recent sources often attribute it to Euclid), such as Mathematically Speaking: A Dictionary of Quotations edited by Carl C. Gaither and Alma E. Cavazos-Gaither (1998), p. 214 http://books.google.com/books?id=4abygoxLdwQC&lpg=PP1&pg=PA214#v=onepage&q&f=false. The earliest publication located that attributes the quote to Kepler is the piece "The Mathematics of Elementary Chemistry" by Principal J. McIntosh of Fowler Union High School in California, which appeared in School Science and Mathematics, Volume VII ( 1907 http://books.google.com/books?id=kAEUAAAAIAAJ&pg=PR3#v=onepage&q&f=false), p. 383 http://books.google.com/books?id=kAEUAAAAIAAJ&pg=PA383#v=onepage&q&f=false. Neither this nor any other source located gives a source in Kepler's writings, however, and in an earlier source, the 1888 Notes and Queries, Vol V., it is attributed on p. 165 http://books.google.com/books?id=0qYXAQAAMAAJ&pg=PA165#v=onepage&q&f=false to Plato. Expressions that relate geometry to the divine "mind of God" include comments in the Harmonices Mundi, e.g., "Geometry is one and eternal shining in the mind of God", and "Since geometry is co-eternal with the divine mind before the birth of things, God himself served as his own model in creating the world".
Disputed quotes

Source: The Hero with a Thousand Faces (1949), Chapter 2, page 87 (New World Library, 2008)
Context: (...) we today (in so far as we are unbelievers, or, if believers, in so far as our inherited beliefs fail to represent the real problems of contemporary life) must face alone, or, at best, with only tentative, impromptu, an not often very effective guidance. This is our problem as modern 'enlightened' individuals, for whom all gods and devils have been rationalized out of existence.