Jihadist fighters in Syria are calling on ISIS to release British hostage Alan Henning, saying that killing him would be “haram” (forbidden in Islamic law).

The Times reports that extremists are openly dissenting over the group’s threat to kill Henning, saying there is no justification for doing so. Abu Dujana al Muhajir, a British fighter, told the paper: “They need to release him to win the hearts of the people,” adding: “I will speak to the brothers in IS [Islamic State] but everyone’s been told to keep quiet. I don’t know what IS have on him. If he is just an aid worker then definitely it is Haram to kill him.”

ISIS have offered up various excuses to justify the killing of the previous three hostages. They said that it was okay to kill James Foley because his brother was in the US air force; Steven Sotloff had dual Israeli citizenship and David Haines had formerly served in Britain’s Royal Air Force.

Another ISIS fighter claimed that Henning had been given safe passage by a Sunni fighter known to the group, meaning that even kidnapping him was haram.

British imams and Muslim leaders have also appealed to ISIS to release Mr Henning. In a video called “#FreeAlanHenning – The Islamic Perspective”, Shaykh Haitham al Haddad, who is a judge in the Sharia Council in London, said that executive Henning would be forbidden in Islamic law.

Ustadh Abu Eesa, director of Prophet Guidance in Manchester also said in the video: “What there is no doubt about is that the killing of an innocent man is not permitted in the religion of Allah, it is not allowed in the religion of Islam.” He added: “However strongly we feel about Western foreign policy, this killing will not help anyone bring closer a solution to their grievances.”

“In Shariah it is not permissible whatsoever to harm a person who believes that he is safe amongst the people that he is working with, whoever it is that granted him that safety. This safety must be honoured,” Abu Ees said. He added that ISIS risked “defacing” Islam if they killed Henning.

The video comes as over 100 Muslim leaders signed a letter calling for Henning’s release. In the letter, they write:

“Mr Henning was a volunteer who travelled to Syria to help innocent civilians.

“Acts of humanitarianism are an essential element of religious practice for all Muslims, and of course they are just as significant to other people too. Islamic teachings call for charity and selflessness. Most importantly, acts of beneficence do not, and cannot, exclude non-Muslims.

“In Islam, concern for fellow humans and the duty to help everyone is a religious obligation. Anyone undertaking a humanitarian act is paving his or her way to receive help from heaven, should be commended and held in the highest esteem.”