Alabama Rules of Appellate Procedure
Rule 47. Agreements in writing
No private agreement or consent between the parties or their attorneys, relating to the proceedings in any cause, shall be alleged or suggested by either against the other, unless the same be in writing, and signed by the party to be bound thereby; provided, however, agreements made in open court or at pretrial conferences are binding, whether such agreements are oral or written.
This is essentially former Supreme Court Rule 20.