“To talk about the end of science is just as foolish as to talk about the end of religion. Science and religion are both still close to their beginnings, with no ends in sight.”

Vol. I, Part 1, [The Materialist Conception of History].
The German Ideology (1845/46)
Context: Where speculation ends — in real life — there real, positive science begins: the representation of the practical activity, of the practical process of development of men. Empty talk about consciousness ceases, and real knowledge has to take place. When reality is depicted, philosophy as an independent branch of activity loses its medium of existence. At the best its place can only be taken by a summing-up of the most general results, abstractions which arise from the observation of the historical development of men. Viewed apart from real history, these abstractions have in themselves no value whatsoever. They can only serve to facilitate the arrangement of historical material, to indicate the sequence of its separate strata. But they by no means afford a recipe or schema, as does philosophy, for neatly trimming the epochs of history. On the contrary, our difficulties begin only when we set about the observation and the arrangement — the real depiction — of our historical material, whether of a past epoch or of the present.

Scientific Autobiography and Other Papers as translated by F. Gaynor (1949), p. 184
Variant translations:
Both religion and science need for their activities the belief in God, and moreover God stands for the former in the beginning, and for the latter at the end of the whole thinking. For the former, God represents the basis, for the latter – the crown of any reasoning concerning the world-view.
Religion und Naturwissenschaft (1958 edition), p. 27, as quoted in 50 Nobel Laureates and Other Great Scientists Who Believe in God (2008) by Tihomir Dimitrov http://nobelist.tripod.com/sitebuildercontent/sitebuilderfiles/50-nobelists.pdf
While both religion and natural science require a belief in God for their activities, to the former He is the starting point, to the latter the goal of every thought process. To the former He is the foundation, to the latter the crown of the edifice of every generalized world view.
Scientific Autobiography and Other Papers (1968 edition)
Religion and Natural Science (1937)

Remark, attributed in John Gordon Stewart Drysdale and John James Drysdale, The Protoplasmic Theory of Life (1874), p. 279 (note).
Sourced but undated

Dissertation for doctor of philosophy in christian education (May 25, 1991)

The Story of Philosophy (1926)

Section 165
Reflections on the Human Condition (1973)
Context: The end comes when we no longer talk with ourselves. It is the end of genuine thinking and the beginning of the final loneliness. The remarkable thing is that the cessation of the inner dialogue marks also the end of our concern with the world around us. It is as if we noted the world and think about it only when we have to report it to ourselves.

Source: Thinking in Pictures: My Life with Autism