Surah 34. Saba

75That is, "They used to charge the Messenger and the believers with false accusations and used to taunt and mock his message. Some times they said he was a sorcerer or a madman; sometimes they ridiculed Tauhid and the concept of the Hereafter; sometimes they invented the story that another one taught him everything; and sometimes they said that the believers had started following him only on account of folly and ignorance "

76As a matter of fact, no one adopts shirk and atheism and denial of the Hereafter by conviction, nor can he, for conviction comes from knowledge. And no one has the knowledge that there is no God, or that many others have a share in Divine authority, or that there should be no Hereafter. Thus, whoever has adopted these beliefs in the world, has raised a structure on mere conjecture, which has no basis except doubt and suspicion, and this suspicion has led him to sheer error. Consequently, they doubted God's existence, they doubted the truth of Tauhid, they doubted the coming of the Hereafter; so much so that they made this doubt their faith and did not listen to the Prophets and expended and wasted their whole lifetime indulging in a wrong creed and way of life.