If you just want the sources at a particular version then they are available here:
http://download.qt-project.org/archive/qt/
without having to clone the entire repository.

If you want to use Git then, once you have cloned the repository, you use the git checkout command:
Qt Code:
  1. $ git checkout tags/v4.8.2
To copy to clipboard, switch view to plain text mode 
(where v4.8.2 is one of the tags in the repository) should do it.