My husband traveled a few times last year on business. He was reimbursed on a per diem rate for meals, but he didn't spend as much as he was reimbursed. Is this taxable?

We didn't receive a separate 1099 for these reimbursements. I just wanted to know if we need to report them as income, particularly meals, as he only spent a little and they reimbursed him for more than that. And if we do report them as income, how do we report them?