Letter to James E. Yeatman of St. Louis, Vice-President of the Western Sanitary Commission (21 May 1865). As quoted on p. 358, and footnoted on p. 562, in Sherman: A Soldier's Passion For Order https://en.wikiquote.org/wiki/Special:BookSources/080938762X (2007), John F. Marszalek, Southern Illinois University Press, Chapter 15 ('Fame Tarnished')
Variant text: I confess, without shame, that I am sick and tired of fighting — its glory is all moonshine; even success the most brilliant is over dead and mangled bodies, with the anguish and lamentations of distant families, appealing to me for sons, husbands, and fathers […] it is only those who have never heard a shot, never heard the shriek and groans of the wounded and lacerated […] that cry aloud for more blood, more vengeance, more desolation. […] I declare before God, as a man and a soldier, I will not strike a foe who stands unarmed and submissive before me, but would rather say—‘Go, and sin no more.’
As quoted in Sherman: Merchant of Terror, Advocate of Peace https://en.wikiquote.org/wiki/Special:BookSources/1455611891 (1992), Charles Edmund Vetter, Pelican Publishing, p. 289
See the Discussion Page for more extensive sourcing information.
1860s, 1865, Letter to James E. Yeatman (May 1865)
Context: I confess without shame that I am tired & sick of war. Its glory is all moonshine. Even success, the most brilliant is over dead and mangled bodies […] It is only those who have not heard a shot, nor heard the shrills & groans of the wounded & lacerated (friend or foe) that cry aloud for more blood & more vengeance, more desolation & so help me God as a man & soldier I will not strike a foe who stands unarmed & submissive before me but will say ‘Go sin no more.