It is narrated from Sayyiduna Uqbah bin Amir al-Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said to Sayyiduna Uqbah: "When you pray, recite these two in your prayer, for you will not recite anything like them", meaning the Mu'awwidhatayn (Surah al-Falaq and Surah al-Nas).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15028