Refer him to
http://www.faithfreedom.org
Here's some information about Mohammad from the book "Understanding Mohammad" by Ali Sina of FFI.
Muhammad is one of the world most influential man indeed, historians tell us Muhammad used to withdraw to a cave, spending days wrapped in his thoughts. He heard bells ringing and had ghostly visions. He thought he was demon possessed, until his wife reassured him he had become a prophet. Convinced of his status, he was intolerant of those who rejected him, assassinated those who criticized him, raided, looted, and massacred entire populations. He reduced thousands to slavery, raped, and allowed his men to rape female captives. All of this, he did with a clear conscience and a sense of entitlement. He was magnanimous toward those who admired him, but vengeful toward those who did not. He believed he was the most perfect human creation and the universe's raison d'être. Muhammad was no ordinary man. Islam is Muhammadanism. Muslims worship and emulate Muhammad. Only by understanding him can one know what makes them tick. Muhammad had a loveless childhood. He then passed to the care of relatives who took pity on him and spoiled him. As the result he developed narcissistic personality disorder, a trait that made him a megalomaniac bereft of conscience. Muhammad believed in his own cause. Even when he lied, he felt entitled and justified to do so. Thanks to another mental illness, namely temporal lobe epilepsy, the prophet of Islam had vivid hallucinations he interpreted as mystical and divine intimations. He also suffered from obsessive compulsive disorder, causing his fixations on numbers, rituals and stringent rules. In the addition, he suffered from acromegaly, a disease caused by excessive production of a growth hormone resulting in large bones and odd facial features. The combination of his psychological disorders and his unusual physiognomy made him a phenomenon that set him apart from ordinary people. His uneducated followers interpreted his differences as signs of his prophethood. Like devotees of all cults, they rose to champion his cause with dedication. By defying death and butchering others they made Islam the world's second largest religion, now the biggest threat to world peace.
