The French news agency, AFP, reports that journalists and lawyers turned up for the scheduled appeal hearing at New Gawu, Niger state, only to find that the two had been freed last week.
Ahmadu Ibrahim said that he and his former lover, Fatima Usman, who is pregnant, only learnt that they had been sentenced to death moments before being released last Thursday.
This is the latest in a series of judgments handed out by Islamic or Sharia courts in Nigeria and which have provoked concern amongst human rights groups around the world.
Nigeria's northern states have introduced Islamic punishments into the criminal code over the past three years.
Click here for a map of Nigeria's Sharia states
Defence lawyer Jibril Kallamu said he had last week brought an emergency motion to secure the couple's release because Ms Usman, 32, was about to go into labour.
"She has gone nine months. She could give birth today, tomorrow, or the day after," he said.
Appeal
The couple was originally imprisoned for the offence of adultery.
But at an appeal hearing, held in their absence, the judge imposed the death sentence, arguing that the earlier court had used the wrong penal code to try the case.
Ms Usman has a two-and-a-half-year-old daughter, allegedly fathered by Mr Ibrahim outside marriage.
She is now pregnant with the child of her former husband, her lawyers say.
At least five death-by-stoning sentences have been passed in northern Nigeria but none of them has yet been carried out.
This is in large measure due to the pressure being put on Nigeria by foreign governments and human rights groups.
But defence lawyers are increasingly concerned that it is only a matter of time before one of the majority Muslim northern states decides to carry out such a sentence.
More than any other, this case highlights the concerns of human rights activists that such cases have been poorly handled by the Islamic courts.
Nigeria's central government has said it is opposed to such sentences being carried out, but says it has no powers to intervene in judgments handed down by Islamic courts in the north of the country.
Related to this story:
No respite for Nigeria stoning couple
(08 Oct 02 | Africa)
More stoning sentences in Nigeria
(29 Aug 02 | Africa)
Nigerian man faces stoning
(27 Aug 02 | Africa)
Nigeria fights Sharia death sentence
(23 Aug 02 | Africa)
Nigeria's stoning appeal fails
(19 Aug 02 | Africa)
Reprieve for Nigerian adultery convict
(03 Jun 02 | Africa)
Internet links:
Sharia law (Christian site)
|
Islam Q&A
|
Amnesty International pro-Amina Lawal campaign
|
Government of Nigeria
The BBC is not responsible for the content of external internet sites