Grant wrote similar letters to Secretary of War Stanton and Chief of Staff of the Army, General Halleck on May 11, 1864, near Spotsylvania, Virginia. In essence, this is what they both said:
"We have entered the sixth day of very hard fighting ... The result to this time is much in our favor ... I propose to fight it out on this line if it takes all summer."
Henry Wing, young reporter for the New York Tribune, was on site at the Battle of the Wilderness, but Grant refused to allow any reports to be sent to the news outlets. Wing told Grant he was leaving to file a story in person. Grant asked him if he was going to Washington, DC. When Wing answered in the affirmative, he asked him, if he saw the President, to tell Lincoln (who was in the dark about this battle and anxious about it) the following:
Whatever happens, there will be no turning back.
Wing brought the message to Lincoln, who was so gratified and relieved to hear his chief general was not going to retreat to Washington, that he bent over and kissed the reporter on his forehead. (Wing, Henry. When Lincoln Kissed Me, Abingdon Press, 1913.)
February 16, 1862
Gen. S. B. Buckner, Confederate Army
Yours of this date proposing Armistice, and appointment of commissioners, to settle terms of capitulation is just received. No terms except unconditional and immediate surrender can be accepted. I propose to move immediately upon your works.
I am sir, very respectfully, Your obt. servt. U. S. Grant, Brig. Gen.
See Ulysses S. Grant, Triumph Over Adversity, 1822-1865, by Brooks D. Simpson. Houghton Mifflin, 2000, p. 112-118, for an excellent narration of the entire Ft. Donelson encounter.
This quote has been attributed to Grant in a variety of sources beginning in the early 20th century, but none in the 19th century.
"The art of war is simple enough. Find out where your enemy is. Get at him as soon as you can. Strike him as hard as you can, as often as you can, and keep moving on."