As-Saffat · 37:37

37. Verily, they have spoken a grave lie, because the Messenger of Allah (peace be upon him) was not a madman nor a poet; he brought the Qur’ān which calls towards the oneness of Allah and towards following His Messenger. He corroborated the message of monotheism and affirmation of the afterlife the messengers brought from Allah; he did not contradict them in anything.