Validate Two Inputs which depends on each other

I have two Inputs 'creditor' and 'debtor' , I want The user to put value in one of them at least, or both.

if($request->input('creditor')==Null && $request->input('debtor')==Null){
        Session::flash('danger','Please add Value in one of the two inputs at least');
        return redirect()->back();
    }

How to do the same thing with laravel validation

via Chebli Mohamed