And it escalated to rape and months of sexual abuse, the now 28-year-old young man says.
"I feel rage now when I think after he raped me he took a bath and right away he left to lead the prayers," the man, an economist who lives in Islamabad, told The Associated Press.
"After that I came to know from three or four of my classmates that the mufti used to do the same with them."
He said he suppressed memories of the abuse for years, but after reading an AP report last month revealing widespread abuse by clerics in Pakistan's thousands of madrassas, they all came tumbling back.
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"I read the story two times. The first time I was shocked. The things that were written there were everything I had lived. The second time I read it, the whole of my body was trembling because of the memories it brought back," said the man, speaking on condition of anonymity, not only because of the shame he felt nearly two decades later but because he feared Pakistan's religious leaders could retaliate against him either with violence or charges of blasphemy or being an apostate, both of which, he said, were tantamount to a death sentence.
"They said 'Stop talking. This is not something to discuss.' It is so common in the madrassas here, but people don't want to talk about it. We are ashamed," the young man said.
There are more than 22,000 registered madrassas in Pakistan, and many thousands of unregistered ones, often grimy one- or two-room facilities in remote villages. The millions of students they teach are often among the country's poorest, who receive food and an education for free.
Naeema Kishwar, a federal lawmaker who last year helped change Pakistan's laws to close a legal loophole that had allowed those who commit so-called "honor killings" to escape punishment, said that laws exist to tackle sexual abuse of minors, which she called a scourge in Pakistan, not only in madrassas but in public schools, at home and among the army of child workers who are employed in homes as domestic workers and in factories.
But Kishwar who is a member of the religious Jamaat-e- Ulema-e-Islam, a pro-Taliban party, took umbrage with a focus on sexual abuse in the madrassas. Her party operates thousands of religious schools. But like the clerics who dominate her party, Kishwar, despite data and evidence to the contrary, said the incidents of abuses in religious seminaries were isolated.
He blamed fear among the mainstream media of antagonising the country's religious leaders and because sex, even if it involves abuse, is a taboo subject.
"Such topics rarely get any coverage on national television channels. And for that reason, there were discussions on social media which were much more encouraging," he said.