Need quick help with Thoth reference (no replies)

In one of Graham's books (likely fingerprints but I am not certain) Graham re-tells the myth of Thoth presenting the invention of writing as a new system of 'knowing' and Ra corrects him and says that instead it is a system of 'remembering'.
Does anyone know what that original source of the myth is as well as in which of his books Graham uses this example?


Thank you all in advance!