You can call me "Al"...

[Angela]

Eva, I recently discussed this on another board.
Apparently there are two sources.

One is William Herndon who wrote:

“Not even Judge David Davis or any or his other intimates felt sufficiently free and easy to call him Abe or slap him on the shoulder”.

The other one comes from Henry Clay Whitney who writes in "Life on the Circuit with Lincoln":

“Although I have heard of cheap fellows, professing that they were wont to address him as ‘Abe,’ I never knew of any one who ever did it in my presence.
Lincoln disdained ceremony, but he gave no license for being called ‘Abe.’
His preference was being called ‘Lincoln’ with no handle at all.”