Dawkins, when discussing the infamous Gnostic Gospels, claims that Thomas Jefferson, in a letter to his nephew, referred to these Gnostic texts and encouraged his nephew to read “all the histories of Christ.” Dawkins writes, “It is these additional gospels that Thomas Jefferson was referring to in his letter to his nephew…” 
However, David Marshall, in this book The Truth Behind the New Atheism, explains the fatal problem with this claim:
"Jefferson was a talented man...But Jefferson did not, I think, claim the gift of prophecy. That would have been required for him to refer to Thomas, Mary or Philip, which were lost in the Egyptian desert at the time Jefferson allegedly recommended them to his nephew." 
Readers may also want to check out Marshall's article The God Delusion: 160 Errors, Gross Exaggerations, and Highly Dubious Claims.
Courage and Godspeed,
1. Dawkins, The God Delusion, p. 95.
2. Marshall, The Truth Behind the New Atheism, p. 122.