Git'ing a non-labeled set of sources

Hello All,

Please excuse me if this is an ignorant question; I'm new to git and my
have overlooked something in the documentation.

I'm attempting to obtain a snapshot of source code from an unlabeled git
branch in a public repository. I've found in the documentation that a
timestamp cannot be used to specify a particular version of source code,
but I believe I can work with the commit value as returned by 'git
show'.

However, I have been unsuccessful in my attempts to use this identifier
to clone or checkout the associated source tree. Has anyone been
successful in using git to successfully replicate an unlabeled version
of sources in a repository?

Here is my latest attempt:
/dir_i_want_to_replicate $ git show --pretty=short
commit 5b1313fb2758ffce8b624457f777d8cc6709608d
Author: ....

/replication_dir $ git clone git://www.denx.de/git/u-boot.git
u-boot-mpc83xx
Blah blah blah..
 100% (4378/4378) done
/replication_dir/u-boot-mpc83xx/ $ git checkout
5b1313fb2758ffce8b624457f777d8cc6709608d
error: pathspec '5b1313fb2758ffce8b624457f777d8cc6709608d' did not match
any. 

Any suggestions would be greatly appreciated.
Thanks in advance,
Sam Sparks