Sayyiduna Uqbah bin Amir (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Verses have been revealed to me the like of which I have never heard" (or he said: "the like of which I have never seen"), meaning the Mu'awwidhatayn (Surah al-Falaq and Surah al-Nas).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15034