Many states permit recording of a conversation provided that one of the parties permits the recording. This varies from state to state. If you recorded the converstaion, that would be permissible. However, I am unaware of a state that permits the recording of a conversation to be used in court without the permission of any of the parties unless there was some court order, which I doubt there was in this instance. The husband was not a party to the conversation.
As a legal strategy, you may want to allow the husband to attempt to "prove" his case with the tape and then object to its being played. It will make the husband appear to have poor character -- can you imagine if your own wife or husband secretly recorded your private conversations?! It is always best to find the appropriate law of your state to make sure that the recording was impermissible and then cite it.