Here is the exact quote. Fortunately, it does give a little more information than I had initially recalled on the flag's wording. I hope it helps in your research.

“The fighting of the first day was mostly on our left and we moved towards it gradually. During the night we fell back, forming a second line. This day Gibson’s La. Brigade occupied the position immediately on the left of the Franklin Pike and Clayton’s Ala. Brigade on the right of it. Here our line was attacked during the day, one of the charges being made by negro troops, which was repulsed. Its line being so badly cut up that they lost their flag. This was a beautiful one with this inscription ‘13th U.S. Colored Inft. presented by the colored ladies of Murfressboro.’”