Mike Jones, a former employee of Carnegie Mellon, started an effort in February 2002 to find Scott Fahlman's original post in which the idea of a smiley was first proposed. After months of detective work, collecting of VAX tape backups and sifting through the data they found Scott's message on September 10, 2002. It was sent to the CMU CS bulletin board system twenty years ago:

19-Sep-82 11:44    Scott E  Fahlman             :-)
From: Scott E  Fahlman 

I propose that the following character sequence for joke markers:


Read it sideways.  Actually, it is probably more economical to mark
things that are NOT jokes, given current trends.  For this, use


Scott Fahlman states himself that this may not be the first use of the smiley (or emoticon) symbol, but no recorded evidence of earlier occurrences have been found so far. In any case, Mike Jones and his team have done a great job bringing this piece of communications history to us.

Sources of information:
"The First Smiley :-)" by Mike Jones, http://research.microsoft.com/~mbj/Smiley/Smiley.html
"Smiley Lore :-)" by Scott E. Fahlman, http://www-2.cs.cmu.edu/~sef/sefSmiley.htm