The execution occurred in Hudur district, Somalia, on July 1.
International Christian Concern (ICC) reported that Muhammad Guul Hashim Idiris, a Christian convert from Islam, was travelling from Kalafo, an Ethiopian border town. He planned to visit his mother in Mogadishu.
ICC said a fellow passenger recognised Idiris' "Christian background" and asked him if he thought the prophet Muhammad was a genuine messenger from God. Idiris responded by saying, "If I thought so, I would have believed in him instead of the Messiah."
Once they reached the Hudur district, ICC said, a stronghold of the Al- Shabaab terror network, the Muslim man reported Idiris to Al-Shabaab and had him detained on June 27. Idiris was accused of insulting the prophet Muhammad. It is a serious sin under Islam to consider Muhammad not to be a genuine prophet and it warrants the death penalty.
ICC said that Sheik Adan Yare, the Al-Shabab governor of the Bakol region, spoke to the press on July 1 and said, "Our holy warriors have today, on July 1 at 11: 45 am, executed in front of angry Muslim witnesses a young man whose name was Muhammad Guul Hashim Idiris who insulted our beloved prophet."
The execution, which took place at a make-shift soccer stadium, was attended by hundreds of people, including school children who were forced to watch the grizzly scene.
ICC said Idiris had been married since Jan 26 and is survived by his pregnant widow.
Idiris' paternal uncle and a Christian convert from Islam spoke to ICC from Addis Ababa, calling the Al-Shabaab execution "further evidence of Al-Shabaab's attempt to eliminate Christianity from among Somali people in the Horn of Africa".
Jonathan Racho, ICC's Regional Manager for Africa, said in a news release, "We are deeply saddened by yet another execution of a Somali Christian. Al-Shabaab and Islamic extremist groups in Somalia have repeatedly vowed to wipe out Christians from Somalia.
"Al-Shabaab has murdered several Christians, chopped off the hands of Muslims suspected of crimes and even stoned Muslim women to death for allegedly committing adultery.
"The cruel and inhumane action of Al-Shabaab shows its complete disregard for human life."