Why was the Messenger, peace be upon him, called a madman?

No prophet came to his people with the call to Tawhid (monotheism) but they accused him of madness, magic, and delusion, in order to turn people away from the religion of Allah. This is what happened with the Messenger (peace be upon him); after he was known for his trustworthiness and truthfulness, they accused him of lying, magic, and madness when he brought them the message. This was the custom of previous nations with their messengers.