Ala. Code § 12-21-163

In civil actions and proceedings, there must be no exclusion of any witness because he is a party or interested in the issue tried, except that no person having a pecuniary interest in the result of the action or proceeding shall be allowed to testify against the party to whom his interest is opposed as to any transaction with, or statement by, the deceased person whose estate is interested in the result of the action or proceeding or when such deceased person, at the time of such transaction or statement, acted in any representative or fiduciary relation whatsoever to the party against whom such testimony is sought to be introduced, unless called to testify thereto by the party to whom such interest is opposed or unless the testimony of such deceased person in relation to such transaction or statement is introduced in evidence by the party whose interest is opposed to that of the witness or has been taken and is on file in the case. No person who is an incompetent witness under this section shall make himself competent by transferring his interest to another.