It was Shiloh. General T.S. Sherman wrote about the encounter in his memoirs. Forrest had charged what he thought was a picket line and ran in to a brigade size force. Sherman was up front with said brigade and said it caused himself to run *** over tea kettle in the mud, and that if Forrest's pistols weren't empty, it would have ended his career right then. Forrest then got shot in the hip, at nearly point blank range, yet still managed to escape.
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Years later, at the Annual Meeting of the Society of the Army of the Tennessee held at Cincinnati, Ohio, April 6-7, 1881, Sherman read a paper he had prepared on the Battle of Shiloh. In this account, he remembered as they approached the ridge, Forrest’s cavalry came down, with a yell, firing away with their pistols, riding over the skirmish line, over the supports, and right among him and his staff. For you see, Sherman was out with the skirmishers and remembered, “Fortunately, I had sent my adjutant, Hammond, back to the brigade to come forward into line quickly. My Aide-de-Camp, McCoy, was knocked down, horse and rider, into the mud,
but I, and the rest of my staff ingloriously fled [italics mine], pell mell, through the mud, closely followed by Forrest and his men, with pistols already emptied. We sought safety behind the brigade in the act of forming 'forward into line,' and Forrest and his followers were in turn 'surprised' by a fire of the brigade which emptied many a saddle, and gave Forrest himself a painful wound, but he escaped to the woods on the south of the road."
Sherman adds in the 1881 paper read before his comrades, "I have seen Forrest since the war; have talked with him about this very matter, and he explained that he was left behind by Breckenridge [sic. Breckinridge] to protect this hospital camp, and if possible to check the pursuit by our forces which was naturally expected after the close of the battle of Shiloh.
I am sure that had he not emptied his pistols as he passed the skirmish line, my career would have ended right there [italics mine]."