The battle of Waterloo was won on the playing fields of Eton.

Do you by chance happen to have the source for this statement by Wellington, where and when it was uttered and in which context ?

This comment was possibly attributed by Mark Twain to Abraham Linclon.

The following may help clarify the question:

"The Battle of Waterloo was won on the playing fields of Eton"

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."