“This battle to save life will eventually be won.”

Source: The Fires of Heaven

Letter from the field of Waterloo (June 1815), as quoted in Decisive Battles of the World (1899) by Edward Shepherd Creasy. Quoted too in Memorable Battles in English History: Where Fought, why Fought, and Their Results; with the Military Lives of the Commanders by William Henry Davenport Adams; Editor Griffith and Farran, 1863. p. 400.
Context: My heart is broken by the terrible loss I have sustained in my old friends and companions and my poor soldiers. Believe me, nothing except a battle lost can be half so melancholy as a battle won: the bravery of my troops hitherto saved me from the greater evil; but to win such a battle as this of Waterloo, at the expens of so many gallant friends, could only be termed a heavy misfortune but for the result to the public.

Source: Leaves of Grass

As quoted in The New York Times (26 December 1886), and in Words on Wellington (1889) by Sir William Fraser, this is almost certainly apocryphal. The first attributions of such a remark to Wellington were in De l'Avenir politique de l'Angleterre (1856) by Charles de Montalembert, Ch. 10, where it is stated that on returning to Eton in old age he had said: "C'est ici qu'a été gagnée la bataille de Waterloo." This was afterwards quoted in Self-Help (1859) by Samuel Smiles as "It was there that the Battle of Waterloo was won!" Later in Memoirs of Eminent Etonians (2nd Edition, 1876) by Sir Edward Creasy, he is quoted as saying as he passed groups playing cricket on the playing-fields: "There grows the stuff that won Waterloo."
Elizabeth Longford in Wellington — The Years of the Sword (1969) states he "probably never said or thought anything of the kind" and Gerald Wellesley, 7th Duke of Wellington in a letter published in The Times in 1972 is quoted as stating: "During his old age Wellington is recorded to have visited Eton on two occasions only and it is unlikely that he came more often. … Wellington's career at Eton was short and inglorious and, unlike his elder brother, he had no particular affection for the place. … Quite apart from the fact that the authority for attributing the words to Wellington is of the flimsiest description, to anyone who knows his turn of phrase they ring entirely false."
Misattributed

Source: War and Peace

Arjuna Ranatunga on Indian cricketer Sachin Tendulkar, Sachin Tendulkar: Quotable quotes on the batting legend http://www.khaleejtimes.com/article/20131112/ARTICLE/311129977/1051.

Georg Alexander von Müller's diary entry (23 March 1918) after the first German successes of the Spring Offensive, quoted in Georg Alexander von Müller, The Kaiser and His Court (London: Macdonald, 1961), p. 344
1910s

"The Problems of Parenthood"
The Life of Birds (1998)