Ala. Code § 12-21-112: Written Contract as Evidence of Debt or Duty; Impeachment Thereof.

Every written contract, the foundation of the action, purporting to be executed by the party sought to be charged, his partner, agent or attorney-in-fact, is evidence of the existence of the debt or that the party undertook to perform the duty for which it was given and that it was made on sufficient consideration, but may be impeached by answer, and, when so impeached, the burden of proof is on the defendant.