This was originally drawn by  rednoodle.inc as a sketch commission. Noodle does great art and the prices were cheap, so I couldn't resist.
I'm mostly posting this because Noodle hasn't posted it to their own gallery, and also because I'm going to submit a colored version I made afterward, so I want something to compare it to. I'll have more details about this piece in that one.
The colored version can be found here: http://www.furaffinity.net/view/18936917/