Four men in Nigeria's northern city of Kano have received death threats for organising a mock wedding on Facebook that was deemed offensive to Islam.The groom, Sanusi Abdullahi, confessed to having "jokingly" offered a female Facebook friend a bride price of $56 (£44) during the "online marriage".Religious leaders said it was a mockery of the institution of marriage.Kano is among 12 northern states where Islamic law, or Sharia, operates, implemented by religious police.Mr Abdullahi, 29, told the BBC that the messages he exchanged with a female Facebook friend about a wedding were in jest.His other friends, who are part of the same group, then joined the conversation - one pretended to give the woman away, the other two acted as "witnesses" to the wedding.The story quickly spread on Facebook and was picked up by local media, leading to condemnation by religious leaders who called for their arrest.Sheik Nazifi Inuwa, a prominent religious leader in Kano, told the BBC that the incident was unIslamic."In Islam only wayward ladies marry out themselves without their parents or guardians giving her out to her suitor. What Sanusi and his friends did is nothing but a useless charade... Islamic marriage is never done like this."Mr Abdullahi and his three friends decided to go into hiding after they started receiving death threats by text message.He was attacked by an unknown person on Monday, an incident that made him and his friends decide to emerge from hiding and report to the Hisbah [religious police] to apologise for the mock wedding.Abba Sufi, the head of Hisbah in Kano, told the BBC that he had accepted the men's apology, and warned them not to do it again."I was afraid after I was attacked but the police have assured me that they will investigate the incident. I am also thankful that it has been two days and I have not received a threat," Mr Abdullahi told the BBC.The woman involved in the incident lives in the north-eastern state of Borno and has not been sanctioned, but her boyfriend has reportedly left her because of the incident.Mr Abdullahi also told the BBC that his fiancée had left him.