To see the diff for a particular  COMMIT hash:

`git diff COMMIT~ COMMIT` will show you the difference between that COMMIT's ancestor and the COMMIT. See the man pages for git diff for details about the command and gitrevisions about the ~ notation and its friends.

Alternatively, `git show COMMIT` will do something very similar. (The commit's data, including its diff - but not for merge commits.) See the git show manpage.