LAHORE, Pakistan — Late one night, the imam Shabir Ahmad looked up from prayers at his mosque to see a 15-year-old boy approaching with a plate in his outstretched left hand. On it was the boy’s freshly severed right hand.

Mr. Ahmad did not hesitate. He fled the mosque and left the village, in eastern Punjab Province.

Earlier that night, Jan. 10, he had denounced the boy as a blasphemer, an accusation that in Pakistan can get a person killed — even when the accusation is false, as it was in this case.

The boy, Anwar Ali, the son of a poor laborer, had been attending an evening prayer gathering at the mosque in the village, Khanqah, when Mr. Ahmad asked for a show of hands of those who did not love the Prophet Muhammad. Thinking the cleric had asked for those who did love the prophet, Anwar’s hand shot up, according to witnesses and the boy’s family.

He realized his mistake when he saw that his was the only hand up, and he quickly put it down. But by then Mr. Ahmad was screaming “Blasphemer!” at him, along with many others in the crowd. “Don’t you love your prophet?” they called, as the boy fled in disgrace.