Musannaf Ibn Abi Shayba 22:298

'Affan narrated to us, he said: Abu Hilal narrated to us, he said: Mansur al-Qassab narrated to us, he said: I asked al-Hasan, I said: "O Abu Sa'id, should I recite the two *Mu'awwidhatayn* (Surah al-Falaq and Surah an-Nas) in the dawn prayer?" He said: "Yes, if you wish; they are two blessed, good surahs."