Most importantly, the letter should be placed on your financial institution's letterhead.
To Whom It May Concern:
Mr. Joe Doe has had an account with our bank since 1995. His account is currently in good standing and he maintains his current relationship with us.
Mr. Doe currently has a combined balance in his checking and savings account of $10,000.
This reference is issued for the interested party and the bank makes no assurances as to the credit worthiness of Mr. Doe. This letter does not impose any responsibility on the bank.