“The Schoolboy, with his satchel in his hand,
Whistling aloud to bear his courage up.”

citation needed
Weekend Update samples

Source: All I Want for Christmas is a Vampire

"On the Educational Value of the Natural History Sciences" (1854) http://aleph0.clarku.edu/huxley/CE3/EdVal.html
1850s
Context: I cannot but think that he who finds a certain proportion of pain and evil inseparably woven up in the life of the very worms, will bear his own share with more courage and submission; and will, at any rate, view with suspicion those weakly amiable theories of the Divine government, which would have us believe pain to be an oversight and a mistake, — to be corrected by and by. On the other hand, the predominance of happiness among living things — their lavish beauty — the secret and wonderful harmony which pervades them all, from the highest to the lowest, are equally striking refutations of that modern Manichean doctrine, which exhibits the world as a slave-mill, worked with many tears, for mere utilitarian ends.
There is yet another way in which natural history may, I am convinced, take a profound hold upon practical life, — and that is, by its influence over our finer feelings, as the greatest of all sources of that pleasure which is derivable from beauty.

The Whistle (November, 1779); reported in Bartlett's Familiar Quotations, 10th ed. (1919).
1770s

The Old Man and the Sea (1952)

Pt. I line 357.
Absalom and Achitophel (1681)

De Re Militari (also Epitoma Rei Militaris), Book I, "The Selection and Training of New Levies"
Context: The courage of a soldier is heightened by his knowledge of his profession, and he only wants an opportunity to execute what he is convinced he has been perfectly taught. (Book 1)