form_validation two is_unique

Hello

I've a little issue, in my view receive one param by post named GatewayId

This is my controller

Code:

$this->load->model("DeleteExpense_model");

   $GatewayId = $this->input->post('GatewayId');

   $this->form_validation->set_rules('GatewayId', 'GatewayId', 'is_unique[tab_expense.tab_gateway_id]');
   $RESULTA=$this->form_validation->run();

   $this->form_validation->set_rules('GatewayId', 'GatewayId', 'is_unique[tab_income.tab_gateway_id]');
   $RESULTE=$this->form_validation->run();

I want to check in two tables, then problem is that return false in both cases, if I run by separate work as well, it should retunr in the first case true and false in the other but seems like the second check overwrite the first, can somebody help me?

Thank you advance!.