Here are four primary sources, in the form of letters.
Calloway, C. J. (1907). Letter from Clinton J. Calloway to Thomas M. Campbell, December 6, 1907 [Personal communication].
Washington, B. T. (1895). Letter from Booker T. Washington to D.C. Gilman, May 18, 1895 [Personal communication].
Knapp, S. A. (1907). Letter from Seaman A. Knapp to the General Education Board, October, 1907 [Personal communication].
Barrow, D. N. (1907). Letter from David N. Barrow to Seaman A. Knapp, December 9, 1907 [Personal communication].