Commit only one file and go over the directory repository

Hello everyone,

I have files added in stage area and this files and another file (e.g. content/content-a95.php) also in working directory.
I need commit the content/content-a95.php, remember, this file was, only, working directory. How can I do the commit specifically to content/content-a95.php? The files in stage should stay there.

On branch master
Your branch is ahead of 'origin/master' by 10 commits.
  (use "git push" to publish your local commits)
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    **new file:   exercises/css/excss31.html**

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

    **modified:   content/content-a95.php**
    **modified:   exercises/css/excss31.html**