“The large benefits which the divine liberality is constantly bestowing on the wicked are preparing them for heavier judgment. As they neither think that these proceed from the hand of the Lord, nor acknowledge them as his, or if they do so acknowledge them, never regard them as proofs of his favor, they are in no respect more instructed thereby in his mercy than brute beasts, which, according to their condition, enjoy the same liberality, and yet never look beyond it.”

Letter to Brigadier-General Nelson, 20 August 1778, in Ford's Writings of George Washington (1890), vol. VII, p. 161. Part of this is often attached to a fragment of a letter to John Armstrong of 11 March 1782; it is also often prefaced with the spurious "governing without God" sentence, as this 1867 example from Henry Wilson (Testimonies of American Statesmen and Jurists to the Truths of Christianity) shows:
It is impossible to govern the world without God. It is the duty of all nations to acknowledge the Providence of Almighty God, to obey his will, to be grateful for his benefits and humbly implore his protection and favor. I am sure there never was a people who had more reason to acknowledge a divine interposition in their affairs, than those of the United States; and I should be pained to believe that they have forgotten that agency which was so often manifested during the revolution; or that they failed to consider the omnipotence of Him, who is alone able to protect them. He must be worse than an infidel that lacks faith, and more than wicked, that has not gratitude enough to acknowledge his obligations.
1770s
Context: It is not a little pleasing, nor less wonderful to contemplate, that after two years' manoeuvring and undergoing the strangest vicissitudes, that perhaps ever attended any one contest since the creation, both armies are brought back to the very point they set out from, and that which was the offending party in the beginning is now reduced to the use of the spade and pickaxe for defence. The hand of Providence has been so conspicuous in all this, that he must be worse than an infidel that lacks faith, and more than wicked, that has not gratitude enough to acknowledge his obligations. But it will be time enough for me to turn preacher, when my present appointment ceases…

Rerum novarum (1891), p. 22

Herbert N. Casson cited in: Forbes magazine (1950) The Forbes scrapbook of Thoughts on the business of life. p. 158
1950s and later

Source: Guide for the Perplexed (c. 1190), Part III, Ch.12
Context: You will see the mercy of God toward His creatures, how He has provided that which is required, in proper proportions, and treated all individual beings of the same species with perfect equality.... for it is an act of great and perfect goodness that He gave us existence; and the creation of the controlling faculty in animals is a proof of His mercy towards them, as has been shown by us.

Letter to John Armstrong, 11 March 1782, in Ford's Writings of George Washington (1891), vol. XII, p. 111. This is frequently attached to part of a letter to Brigadier-General Nelson of 20 August 1778, as in this 1864 example from B. F. Morris, The Christian Life and Character of the Civil Institutions of the United States, pp. 33-34:
I am sure that there never was a people who had more reason to acknowledge a divine interposition in their affairs than those of the United States; and I should be pained to believe that they have forgotten that agency which was so often manifested during the Revolution, or that they failed to consider the omnipotence of that God who is alone able to protect them. He must be worse than an infidel that lacks faith, and more than wicked that has not gratitude enough to acknowledge his obligations.
1780s

Chap. II.
The Theory of Moral Sentiments (1759), Part V

Page 35.
Golden Booklet of the True Christian Life (1551)

Source: Small is Beautiful: A Study of Economics As If People Mattered (1973), p. 35.