Many instances come from their speeches.
Adams’ 1790 comment on the French Revolution, “I know not what to make of a republic of 30 million atheists.”
OUR CONSTITUTION WAS MADE ONLY FOR A MORAL AND RELIGIOUS PEOPLE.
-President John Adams to the Officers of the First Brigade of the Third Division of the Militia of Massachusetts, 179
President Washington said much the same thing in his “Farewell Address”: “Of all the dispositions and habits which lead to political prosperity, religion and morality are indispensable supports. . . . And let us with caution indulge the supposition that morality can be maintained without religion.”
Jeffersons famous “Bill for Establishing Religious Liberty” declares us to be “well aware . . . that Almighty God hath created the mind free,” and suggests that disestablishment is what religion demands.
Adams declared that “In spite of Bolingbroke and Voltaire, I will insist that the Hebrews have done more to civilize men than any other nation.” And he continued, “If I were an atheist . . . I should believe that chance had ordered the Jews to preserve and to propagate to all mankind the doctrine of a supreme intelligent, wise, almighty sovereign of the universe, which I believe to be the great essential principle of all morality, and consequently of all civilization.”
Adams reasoned, “there can be no philosophy without religion.”
1 JA, The Works of John Adams, ten vols. (Boston: Little and Brown, 1850-1856), IX: 229. The Works of John Adams is available here:http://oll.libertyfund.org/index.php?option=com_staticxt&staticfile=show.php&title=2098
2 George Washington, “Farewell Address,” in Washington: Writings, John Rhodehamel, ed. (New York: Library of America, 1997), 971. Also available at: http://teachingamericanhistory.org/library/index.asp?document=82
3 JA to Price, Works of JA: IX
4 Thomas Jefferson, “Virginia Statute Establishing Religious Liberty,” in Jefferson: Writings, Merrill Peterson, ed. (New York: Library of America, 1984), 346. Also available at: http://teachingamericanhistory.org/library/index.asp?document=950
5 JA in Works of JA, IX:609.
6 JA to TJ, July 15, 1813, In Lester J. Cappon, ed., The Adams-Jefferson Letters (Chapel Hill: University of North Carolina Press, 1959), p. 358.
7 JA, “Novanglus,” No. 7, in Works of JA, IV:106. Adams used this definition in all his major writings of the 1770s and 1780s.
8 Cicero in Defence, Works of JA, VI:56.
9 JA, Defence of the Constitutions, Works of JA, VI:185.
10 The Constitution of Massachusetts, in Works of JA, IV:259, 227.
The Question implies that the founding fathers weren't Christian?