MÜNSTER, Germany -- Muhammad Sven Kalisch, a Muslim convert and Germany's first professor of Islamic theology, fasts during the Muslim holy month, doesn't like to shake hands with Muslim women and has spent years studying Islamic scripture. Islam, he says, guides his life.

So it came as something of a surprise when Prof. Kalisch announced the fruit of his theological research. His conclusion: The Prophet Muhammad probably never existed.

Muslims, not surprisingly, are outraged. Even Danish cartoonists who triggered global protests a couple of years ago didn't portray the Prophet as fictional. German police, worried about a violent backlash, told the professor to move his religious-studies center to more-secure premises.

"We had no idea he would have ideas like this," says Thomas Bauer, a fellow academic at Münster University who sat on a committee that appointed Prof. Kalisch. "I'm a more orthodox Muslim than he is, and I'm not a Muslim."

When Prof. Kalisch took up his theology chair four years ago, he was seen as proof that modern Western scholarship and Islamic ways can mingle -- and counter the influence of radical preachers in Germany. He was put in charge of a new program at Münster, one of Germany's oldest and most respected universities, to train teachers in state schools to teach Muslim pupils about their faith.