Previous Employer owes us money

My husband's previous employer owes my husband $10,000.00. My husband worked for a computer/business career college these past six years. The past two years, he was overseeing three facilities. The employer's son was in charge of all the facilities that they owned (franchise). The employer's son verbally promised my husband compensation for overseeing the third facility as the previous manager/facilitator had quit. Then the son quit the business two months after he made the promise. He had told his father of his promise though so the employer was fully aware and agreed to it. The owner is now trying to get out of paying my husband saying he does not have the money. This was while my husband was employed by this man. My husband has since left his job in November to pursue another field of work. My husband was patient and even made up monthly payment schedule to ease the process so that the man wouldn't have to pay in one lump sum. He is still trying to avoid making any payment to us. What legal rights do we have? We have saved all emails that has been used in correspondence.