Qur'an, Al-A'raf, Surah 7:184-186
Has it ever occurred to these people that I, Muhammad, who am their compatriot, am no lunatic? Do they not realize that I am giving a plain warning to them? Will they not ponder on the kingdom of the heavens and the earth, on all that God has created, to discern whether their doom is drawing near? And if they deny these revelations, what revelations will they believe? No one can guide those whom God leads astray. He abandons them, and they blunder about in their wickedness.