"ISIL executed Ibrahim Qassum, a heating oil vendor, by shooting him in the head... on allegations of blasphemy, two days after their forces arrested him," the Syrian Observatory for Human Rights said on Monday.
According to the activists, the man, reportedly suffering from mental illness, was arrested by ISIL militants in the city of Saraqeb, in western Syria, after they accused him of diluting his fuel.
"The fighters bought fuel from him and asked him why it was impure. He responded in the colloquial dialect by saying 'How should I know? What am I, the God of fuel?'" the Observatory said.
The Observatory added that the militants then arrested Qassum, executed him and on Sunday threw his body, with several bullet wounds to the head, in the streets of the town.
In June, the Observatory said ISIL had executed a teenager in front of his parents after accusing him of blasphemy.
RA/NJF