Enbiya 4-5:

• De ki:' Benim Rabbim, yerde ve gökte konuşulan her şeyi bilir. Her şeyi işiten ve her şeyin aslını bilen O'dur'.
  Onlar, (peygamberlerin söylediklerinin) bazen karma karışık rüyalar, bazen kendi uydurması bazen de şiir olduğunu söyleyip durdular, ' Önceki peygamberlere geldiği gibi, bize bir mucize getirsene!' diye de eklediler. 
  (
  This contains a concise answer to the demand for a sign to the effect
  
  (1) You ask for Signs like the ones which were shown by the former Messengers but you forget that those obdurate people did not believe in spite of the Signs shown to them.
  
  (2) While demanding a Sign, you fail to realize that the people, who disbelieved even after seeing a Sign, were inevitably destroyed.
  
  (3) It is indeed a favor of Allah that He is not showing the Sign as demanded by you. Therefore, the best course for you would be to believe without seeing a Sign. Otherwise, you will meet the same doom that the former communities met, when they did not believe even after seeing the Signs. ET
  )