Laravel : how can I fetch all the users who have posts using the eloquent relationship?

I'm trying to learn eloquent relationships. My relation is something like: Users hasMany posts and a post belongs to a user.

when I run my queries in tinker it shows errors.

Error: Exception with message 'Property [post] does not exist on this collection instan
ce.'

$user->new User;
$user->all(); //Displays all the users
but i cannot do
$user->all()->posts;

How can I achieve something like I want to have the users associated with posts or precisely I want users who have written posts.

via Chebli Mohamed