wp-disallow-user-from-seeing-other-users-posts.php

<?php

// disallow users from accessing other users posts
function posts_for_current_author($query) {
	global $pagenow;

if( 'edit.php' != $pagenow || !$query->is_admin )
  return $query;

if( !current_user_can( 'manage_options' ) ) {
  global $user_ID;
  $query->set('author', $user_ID );
}
 return $query;
}
add_filter('pre_get_posts', 'posts_for_current_author');

?>