Connie, explain it as best you can. For example, I have cited things like:
* Memory of John L. Smith, as related to his daughter Jillaine, December 25, 1998, Solana Beach, California.
* Personal knowledge of Henrietta Albert Sess, Laguna Hills, California, as communicated in a letter to her daughter, Eleanor, dated 27 August 1967. Original letter in personal archives of Craig Dye, Washington, DC.