
Letter to Judge J. A. Wakefield, after the death of Lincoln's son Willie in 1862, as cited in Abraham Lincoln: was he a Christian? (1893), p. 292 http://books.google.com/books?id=x8BHAAAAIAAJ&pg=PA292&dq=%22unsoundness+of+the+Christian+scheme%22, by John Eleazer Remsburg. Historian Merrill Daniel Peterson states in Lincoln in American Memory (1994), p. 227 http://books.google.com/books?id=D_FjY_ARcGoC&lpg=PA227&vq=%22Judge%20J.%20A.%20Wakefield%22&pg=PA227, that the letter has never actually been produced to verify the statement and that there's no correspondence with Wakefield noted in the Collected Works.
Misattributed