Alabama Code Title 11. Counties and Municipal Corporations § 11-97-11

All moneys derived from the sale of any bonds issued by a corporation shall be used solely for the purpose or purposes for which the same are authorized;  provided, however, that if for any reason any part of such proceeds shall not be necessary for such purposes, then such unexpended part of such proceeds shall be applied to the payment of the principal or of interest on the said bonds. All accrued interest and premium received in any such sale shall be applied to the payment of interest or principal on the bonds sold.