Daniel Marchenkov

public function comments()
   {
        return $this->hasMany('App\Comment');
   }

public function store(Request $request)
    {
        $post = Post::findOrFail($request->post_id);
    	$post->comments()->create([
           'author_id' => \Auth::user()->id,
           'comment' => $request->comment
        ]);

        return redirect()->back()->with('success', 'Комментарий добавлен');
    }